How to Collect Phone Numbers on Your Website for SMS

Most guides on collecting phone numbers spend their length on short codes and text-to-join keywords. For a store that already has traffic, almost none of the volume comes from there. The numbers come from the same forms that collect emails, asked at a moment when the visitor has already engaged.

This guide covers the website side in detail: where to put the ask, how to sequence it after the email, what the completion rates look like at scale, and what the consent text has to say so the numbers are usable.

Here is what follows:

• Why buying phone number lists does not work

• Where phone numbers actually get collected on a website

• How to write the phone opt-in so people finish it

• Consent rules for numbers collected on a website

• Getting the numbers into your SMS platform

• Apps for collecting phone numbers

• Where to start

Why buying phone number lists does not work

Buying a list of cell phone numbers and sending promotions to it is the fastest way to end an SMS program before it starts.

Purchasing the list is not itself illegal. Texting people who never opted into your program is. The Telephone Consumer Protection Act requires prior express written consent before a marketing text, and a bought list carries no consent that names you as the sender.

Statutory damages run at $500 per message, rising to $1,500 for a willful violation, with no cap on the total. A single campaign to 10,000 unconsented numbers puts the theoretical exposure in the millions.

The commercial damage arrives sooner than any lawsuit. Carriers filter traffic that generates complaints, so a list with poor consent gets your sending number blocked, and the messages that do land reach people who associate your brand with spam.

Two related sources fail for the same reason:

• Numbers collected at checkout for delivery updates. A phone number given so an order can be delivered is not consent to receive marketing.

• Numbers already on your email list. An email subscriber has not agreed to be texted, even when the number sits in the same record.

Both cases need a fresh, separate opt-in. Asking for one is the whole subject of this guide.

Ways to collect phone numbers on websites

A website gives you six places to ask, and they differ in how much intent the visitor has already shown. Sequence matters more than format, because the same request converts very differently depending on what the visitor has already done.

Each of the six below is covered in detail after the summary.

These are the placements, ordered by how much volume they produce for a store with existing traffic:

Ask for the phone number in a second step, after the email

The single change that produces the most numbers is moving the phone field off the first screen and onto a second one.

Two things happen when you do. The first screen keeps its highest possible completion rate, because a form with one field converts better than a form with two. And the visitor who reaches the second screen has already given something, so the next request costs them less.

This only works if the form saves each step on submission rather than at the end. A visitor who gives an email and then closes the popup should still land in your list as an email contact.

A working example of the sequence: Nutrimuscle’s welcome popup asks for the email on step one, the phone number alongside sport type and training frequency on step two, then returns a discount code and matched product recommendations on step three.

Their phone step collects at these rates:

Step one asks for the email against a discount code:

Step two is where the phone number is requested, next to sport type and training frequency:

The profile data collected next to the number is what makes the later text relevant rather than generic. Step three returns the code and product recommendations matched to the answers, so the visitor gets something on the screen where they finish.

The pattern holds at larger volumes. Emma Sleep runs the same sequence across more than 20 markets, where 40.8% of visitors who complete the email step go on to complete the SMS step, for more than a million phone numbers.

For the mechanics of building this kind of form, see the multi-step popup guide.

Add a phone field to a form that already collects email

If you would rather not rebuild a campaign, adding a phone field to an existing signup form takes one action in most builders. In Wisepops you click the form, add a field, and select Phone.

Set expectations before you do it. Every field on a single screen costs completion, so a phone field sitting next to the email field will reduce email signups unless you mark it optional.

Optional is a reasonable trade when volume matters more than the completion rate, for example on an account page where the visitor is already logged in and motivated.

Maison Lejaby collects both in one form, with the phone number as a second field rather than a second step:

Run a phone-only campaign where you already have the email

A phone-only campaign skips the email entirely. Wisepops has a dedicated Phone block for this, so the popup contains a single phone field and its consent text.

Targeting is what makes it work. Show it to visitors who are logged in or arriving from an email link, exclude anyone already subscribed to SMS, and the campaign only ever asks people who can add something.

Without that exclusion the campaign spends most of its impressions on people who already gave you the number, which drags the measured rate down and irritates subscribers. The popup targeting guide covers the rules to set.

Use a tap-to-text link instead of a form field on mobile

Typing a phone number on a mobile keypad is the most tedious part of any signup. A tap-to-text link removes it.

The mechanism is a plain sms: link with a pre-written body. When the visitor taps it, their messaging app opens with the opt-in message already composed and your number in the recipient field, so they only press send.

The link looks like this:

• sms:+18664504185&body=Subscribe%20me%20to%20receive%20updates%20from%20BRAND

You put that link on a button inside a popup, a bar, or an embedded block, and the visitor never types a digit. Their number arrives with the inbound message, which doubles as your consent record.

The trade is that you lose the field-level data a form would collect, and the visitor still has to complete the send.

Whether that trade is worth it depends on your traffic mix. Mobile sessions account for 85% of traffic on Nutrimuscle’s store, which is typical for consumer ecommerce and makes the keypad problem worth solving. See mobile popup best practices for the rest.

Put the ask where intent is already high

Trigger and page choice change the capture rate more than any design decision. Across Wisepops campaigns, a request that fires the moment someone lands performs worst, and one that fires after a deliberate click performs best.

These are the average conversion rates by trigger:

Page targeting matters just as much. Campaigns limited to specific pages convert at 5.53% against 2.40% for campaigns shown everywhere, because the message can match what the page is about.

Which pages win differs by catalog. On Nutrimuscle’s store, collections pages reach 15.4% click-through and account pages 10.2%, ahead of product pages at 6.8%, so the highest-intent page is not always the obvious one.

Keep an embedded form and a bar running in the background

Popups carry the volume, but a share of visitors will never see one. Some dismiss campaigns by habit, some arrive on pages where you suppress popups, and some hit frequency caps.

Two formats catch that traffic without another interruption:

• Embedded signup forms placed in the footer, on the account page, or inside a relevant article. They sit in the page and stay available for the whole session.

• A sticky bar pinned to the top or bottom of the page, which suits returning visitors who already closed a popup once.

Neither will match a well-triggered popup on rate. Both cost nothing to leave running, and they collect from visitors the popup cannot reach.

Collect at the out-of-stock moment

A visitor looking at a product with no stock has shown the clearest possible intent and has no way to act on it. That is the strongest phone-number ask on the whole site, because a text is the right way to tell someone stock has returned.

Trigger the campaign on inventory state so it only shows where stock is actually out, and re-engage the contact when the item returns. The offer writes itself: you are not trading a discount for a number, you are asking so you can tell them when they can buy.

The same logic applies to preorders, restock waitlists, and limited drops.

How to write the phone opt-in so people finish it

Once the placement is right, the wording and the friction around the field decide the rest. Four things reliably change the rate.

Remove the exit from the phone step

By the time a visitor reaches the phone step they have already submitted an email, so anything that offers them a way out is competing with your form.

Emma Sleep tested exactly this on their SMS step, running one variant with a line of dismissal text and one without:

Keep a real close control, because a popup with no way out fails accessibility and Google’s interstitial guidance. What you drop is the extra copy that talks the visitor out of finishing.

Say what the texts are and how often they arrive

“Get SMS updates” asks someone to accept an unknown number of messages about unknown things. “Two texts a month: restocks and early access to sales” is a defined commitment, and it doubles as part of your required disclosure.

Frequency in the opt-in also reduces later opt-outs, because the first few messages match what was promised.

Frame the incentive as a percentage where you can

One test on an exit popup put a percentage discount at a 2.59% signup rate against 2.20% for a fixed amount over 89,000 impressions, an 18% difference from the framing alone.

The same reframing costs nothing to test on a phone step. If your margin structure makes a fixed amount the better offer, keep it and test the wording instead.

Ask for one thing per screen

A phone step that also asks for a birthday and a category preference is a form, not a step. Nutrimuscle groups the phone number with two profile questions and it works, but that step sits behind a completed email and an explicit reward on the screen after.

If your step three has nothing to give, move the profile questions out and ask for the number alone.

If you have nothing to give at the end, ask for the number alone. The micro-commitment principle is that each request should be smaller than the one the visitor just completed.

Consent rules for numbers collected on a website

Consent is what separates a phone list you can send to from a liability. The rules below are the ones that apply to the form itself, which is the part you control on your own site.

None of this is legal advice, and an SMS program crossing several states or countries deserves a review with counsel.

What the form has to do

In the United States, a marketing text needs prior express written consent, and the checkbox that captures it has to meet a few conditions:

• The consent for SMS is separate from the consent for email. One checkbox covering both channels does not give you either.

• The box is unchecked by default. A pre-ticked box is not consent.

• The disclosure sits next to the submit button in readable text, not behind a link the visitor never opens.

• The disclosure names who is sending, states message frequency, notes that message and data rates may apply, says that consent is not a condition of purchase, and explains how to stop.

• Links to your terms and privacy policy are present and working.

Store the record, not just the flag. Keep a timestamp, the page URL, the exact wording that was displayed, and the submitted value, because a consent record you cannot reproduce is not much of a defense.

What has to happen after they subscribe

Opt-out handling has tightened. A subscriber can revoke consent through any reasonable method, so you cannot require a single keyword, and requests have to be honored as soon as practicable and no later than 10 business days after receipt.

Real-time processing is the working standard, since anything slower means live sends to people who already asked you to stop.

A few more rules shape the program rather than the form:

• You may send one clarification message after a revocation, and it cannot contain promotional content.

• Sending windows run from 8am to 9pm in the recipient’s local time.

• The CTIA Messaging Principles are not law, but carriers apply them. Traffic that breaks them gets filtered, which is operationally the same as a penalty.

• US sending numbers need brand and campaign registration through A2P 10DLC before volume traffic will deliver.

• Several states are stricter than the federal baseline, including Florida, Oklahoma, and Maryland, and Texas added requirements in 2025.

Outside the US, the EU and UK treat a phone number as personal data under GDPR, so consent has to be freely given, specific to the channel, and as easy to withdraw as it was to give. The UK adds PECR rules for direct electronic marketing.

The practical consequence for your form is the same in both regions: separate boxes, clear purpose, no bundling with a purchase. Our guide to GDPR and signup forms goes through the wording.

Double opt-in, and when it is worth the drop-off

Double opt-in sends a confirmation text the subscriber has to reply to or click before they join the list. You lose some of the people who submitted the form, and you gain a list where every number is confirmed reachable and every consent is twice recorded.

Some markets require it outright. If you sell across borders, the pattern to build is a flow that switches double opt-in on and off per market rather than one global setting.

Getting the numbers into your SMS platform

A phone number sitting in a form export is not a subscriber. Four things need to happen between the submit button and the first text.

Sync in real time, not on a nightly export

The welcome text works when it arrives while the visit is still fresh, which means the number has to reach your SMS platform on submission.

Wisepops connects to Attentive, Postscript, Klaviyo, Braze, Ometria, Sendlane, and Omnisend among others, with the number and its consent field mapping across as the form is submitted. The full list sits on the SMS integrations page.

Splitting channels across two platforms is normal, and one form can feed both. Emma Sleep sends email to Ometria and SMS to Attentive from a single popup.

Pass the consent field, not just the number

Most platforms have a dedicated field for marketing consent. Map your checkbox to it rather than importing every submitted number as subscribed, because a number in the list without a consent flag is a number nobody can safely send to.

Stop showing the campaign to people who already subscribed

Suppress traffic arriving on your CRM’s UTM parameters so subscribers clicking through from an email or a text never see the acquisition campaign. Add one exclusion rule per sending platform and apply it to every capture campaign.

The benefit is on both sides: your rates stop being diluted by impressions that could never convert, and your existing subscribers stop being asked for something they already gave.

Report phone numbers as their own metric

Campaign reporting that folds phone numbers into total signups hides the step where you are actually losing people. Track the phone step separately, against both impressions and email submissions, so a drop in the second number tells you the step needs work rather than the whole campaign.

Apps for collecting phone numbers

Collecting the number and sending the text are usually two different products. Three that come up most often for stores:

• Wisepops handles the capture side onsite: multi-step popups, embedded forms, bars, a dedicated phone block or a phone field added to a form you already run, plus the targeting that keeps the ask away from people who already subscribed. Numbers sync to your SMS platform as the form is submitted rather than being sent from here.

• TxtCart is an SMS app built for Shopify, installed from the Shopify App Store in one click and free to install. AI agents hold two-way conversations to recover abandoned carts and checkouts, with compliance handling included, and pricing is tied to attributed sales rather than a flat fee. Worth a look if you are on Shopify and want to test whether SMS pays back before committing to a monthly cost.

• Postscript is a Shopify-focused SMS platform for running campaigns and automated flows once the list exists, priced per message sent. Wisepops syncs directly to it, so the capture campaign and the sending platform can be chosen independently.

Whichever sender you pick, something still has to collect the numbers. Most stores end up running one of each rather than expecting a single app to do both well.

Where to start

If you are starting from an email-only program, nothing below touches the campaigns that already work.

Run these in order:

1. Add an SMS step to your best-performing email campaign, after the email is submitted, with its own consent box and disclosure. Leave the first screen untouched.

2. Connect the sync to your SMS platform and map the consent field before you publish.

3. Run it for a full traffic cycle and read the phone step against email submissions, not against impressions.

4. Test the dismissal text on the phone step first, then the incentive framing. Those are the two changes with the clearest recorded effect.

5. Add the out-of-stock campaign next, because the intent is highest there and the ask needs no discount.

6. Leave an embedded form and a bar running to catch visitors the popup never reaches.

If you want to know which of your segments would respond to an SMS ask before you build anything, our team can review your traffic and show you where the volume sits.

Frequently asked questions

Do I need a special phone number to send marketing texts?

You need a number registered for application-to-person traffic, not a personal mobile. In the US that means a 10DLC number registered through A2P with your brand and campaign, a toll-free number, or a short code for high volume. Your SMS platform provisions and registers it as part of onboarding.

Can I text customers who gave me their number at checkout?

Not for marketing. A number given so an order can be delivered is consent for transactional messages about that order. Marketing texts need a separate opt-in with its own disclosure, which is why the checkout page is a good place to put an optional marketing checkbox.

Is it legal to buy a list of phone numbers?

Buying the list is not illegal in itself. Sending marketing texts to numbers on it is, because those people never gave you consent. Statutory damages run $500 per message and up to $1,500 for a willful violation, with no cap on the total.

Should the phone field be required or optional?

Optional if it shares a screen with the email field, required if it has a screen of its own. A required phone field next to a required email field reduces the number of emails you collect, and email is still the larger channel for most stores.

Does asking for a phone number reduce email signups?

Only when both requests share a screen. Asked as a second step after the email is submitted, the phone request cannot cost you emails, because the email is already saved. On one multi-market campaign, 40.8% of visitors who completed the email step went on to complete the SMS step.

How many phone numbers should a website collect?

Use two measurements rather than one. On a large multi-market campaign the SMS step collects 2.3% of impressions, and 40.8% of the visitors who reach it. The second figure is the one to improve, because the first is capped by how many people complete the step before it.

What is the fastest way to collect phone numbers on a Shopify store?

Add a phone step to the welcome popup you already run, then connect it to your SMS platform. See the welcome popup examples for formats, and the quiz popup guide if you want the profile data too.