How to Create and Use an Extension Number Pool

Ever since the invention of the telephone in 1878, businesses have been communicating with the power of voice. Since 1882, companies have been using internal private switches to route calls - this is now commonly known as a PBX.

In the old days, in order to route calls, switchboard operators would manually connect wires from the caller to the destination. Similar to switchboard operators, Retreaver Extensions is bridging the PBX technology of old with the Internet. This will allow you to follow your customers' journey interacting with your company, telling you everything they have done, and everything they need - all with only one phone number for your entire organization.

Extensions can be used to provide cost effective, accurate attribution, provide personalized customer experiences or promotional codes. Assign extensions to individual offers, support agents, sales reps or to VIP customers. The applications are only limited by your imagination. Analyze all your lead sources without having to purchase and track thousands of numbers

How Extensions work

Having a Number Pool with Extensions allow you to create virtual phone numbers that work just like other phone numbers, allowing you to track many different visitors without paying the monthly costs associated with having thousands of phone numbers.

The easiest way to start using extensions is to create a number pool that creates extensions automatically based on the various attributes passed via your landing page. 

There's no need to use the standard +18005550123 x 3444 format, you can phrase it any way you want. You'll probably see higher conversion rates if you call it an exclusive offer id, offer number, promo code, customer id, or listing id. Just a name that's relevant to your business. You might have the prompt say something like:

"Please enter your 4 digit Customer id so we can route your call."

Creating a Number Pool Using Extensions

In the left menu, go to Number Pools and select + New Number Pool. From here, click the toggle for Extensions.


We suggest setting an extension length of four digits since this allows up to 9000 extensions while keeping the user from needing to enter a lot of numbers. You can always increase the extension length later, but it cannot be decreased, so we recommend that you start small.

Please note, if you require more than 2000 extensions, let a Retreaver admin know so this can be enabled on your account.

Setting a base Number

Each extension number pool will require a base number to be set - all extensions will be based on this number. You can create a new base number to be associated with a campaign, or you can choose an existing number. You can leave the toll-free prefix field blank if the prefix doesn't concern you.

Display Numbers with Extensions on your website

Using our Retreaver.js JavaScript library you can easily display extensions on your website, and even make the links clickable for users on mobile devices.

In the example below, a number is requested from Retreaver, and then pop the number with the extension into a mobile-ready link.

We've linked the number in format tel:+18005550123,,5000 where 5000 is the extension. This causes iOS devices to automatically enter the extension and route your caller automatically, just like with any normal phone number.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
<html xmlns="" xml:lang="en">
    <meta http-equiv="Content-Type" content="text/html;charset=UTF-8"/>
    <title>Extension Example</title>
    <script src="" type="text/javascript"></script>
    <script src="" type="text/javascript"></script>
        $(document).ready(function () {
            var campaign = new Retreaver.Campaign({ campaign_key: '48e7931d0bcedc823a6028e6e9ce555a' });
            var tags = {};
            campaign.request_number(tags, function(number) {

                var click_to_call = 'tel:' + number.get('number') + ',,' + number.get('extension');
                $('.click-to-call').attr('href', click_to_call);
    <a href="#" class="click-to-call">
        <span class="number"></span> x <span class="extension"></span>

Bypassing Extensions

Bypassing Extensions can only be done on mobile, you can hyperlink the number as displayed below:

<a href=“[plain_number],,[extension]”>Call [number] using Promo ID: [extension]</a>
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