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Virtual numbers are UK phone numbers that live entirely in software. Unlike a traditional landline or mobile number, a virtual number has no physical line, no SIM card, and no hardware tied to it. Calls are delivered over your internet connection using the SIP (Session Initiation Protocol) standard, which means you can answer calls on a laptop, a mobile app, a desk phone, or any SIP-compatible device — wherever you happen to be. On Kallin, virtual numbers are first-class citizens. They support the full range of routing rules, ring groups, IVR menus, and voicemail features, just like any geographic or mobile number you connect from a traditional carrier.

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What is a Virtual Number?

A virtual number is a standard UK phone number — it can be a geographic 01/02 number, a national 03 number, or another format — that routes calls over the internet rather than through a physical telephone exchange. There is no carrier in the traditional sense. You do not need a contract with BT, Vodafone, or any other network operator to use a virtual number. When someone dials your virtual number, the call travels over the public telephone network as normal until it reaches Kallin’s platform. From there, it is delivered to you as a VoIP call via SIP. To the caller, it looks and sounds like any other UK phone call.

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Use Cases

Virtual numbers suit a wide range of business scenarios:
  • Remote and home workers — give each team member their own UK number that rings on their laptop or mobile app, regardless of where they are working.
  • Customer service lines — provision a dedicated inbound number for your support or sales team without needing a physical office phone system.
  • Temporary campaign numbers — create a number for a specific marketing campaign, track its call volume, and retire it when the campaign ends — all without a long-term contract.
  • International teams with a UK presence — allow overseas staff or contractors to answer UK calls as if they were in a local office, keeping response times fast and costs low.
  • Multi-site businesses — add virtual numbers for new locations or departments instantly, without waiting for an engineer visit or line installation.

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How to Add a Virtual Number

1

Go to Numbers > Add Number

In the Kallin dashboard, navigate to the Numbers section in the left-hand menu and click Add Number.
2

Select 'Virtual / VoIP'

Choose Virtual / VoIP as the number type. You will see a list of available UK number ranges to choose from, including geographic area codes and national 03 prefixes.
3

Choose a UK number range

Pick the number range that suits your needs — for example, a London 020 number for a local presence, or a national 03 number for a UK-wide image. Select an available number from the list and confirm your choice.
4

Configure your SIP credentials or use Kallin's softphone app

Kallin generates SIP credentials for your new number automatically. You can enter these into any SIP-compatible phone, app, or PBX system. Alternatively, download and log in to the Kallin softphone app on your desktop or mobile to start taking calls immediately — no additional configuration required.

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SIP Credentials

When you add a virtual number, Kallin provides you with three pieces of information that let any SIP-compatible device connect to your line:
  • SIP username — a unique identifier for your virtual number on Kallin’s platform.
  • SIP password — a secure credential that authenticates your device when it registers with the platform.
  • SIP server address — the Kallin server your device connects to in order to send and receive calls.
You can find these credentials in the dashboard under Numbers > [your virtual number] > SIP Settings. Enter them into your chosen SIP phone, softphone application, IP desk phone, or third-party PBX (such as Asterisk or FreePBX) and the device will register with Kallin and begin receiving calls. If you regenerate your SIP password, remember to update it in every device that uses those credentials, or those devices will stop receiving calls until they are updated.
Virtual numbers rely entirely on your internet connection for call quality. A stable, low-latency broadband or Wi-Fi connection gives you clear, reliable calls. On congested or slow connections, you may experience audio quality issues or dropped calls. For business-critical lines, a wired ethernet connection or a network with Quality of Service (QoS) settings prioritising voice traffic is strongly recommended.

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Explore Further

VoIP Providers

Connect virtual numbers from your existing VoIP provider, or learn which providers Kallin integrates with directly.

Call Routing

Set up routing rules for your virtual numbers — forward calls, build ring groups, and configure out-of-hours handling.