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VoIP numbers are increasingly common for UK businesses of all sizes, offering flexibility, lower call costs, and easy scalability. If your number is hosted by a VoIP provider, you can connect it to Kallin using either SIP trunking — the recommended approach — or standard call forwarding. Once connected, Kallin handles your routing, IVR, voicemail, and analytics on top of your existing VoIP number, with no need to change your number or leave your current provider.

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Supported VoIP Providers

The following UK and internationally-operating VoIP providers are supported. Where multiple connection methods are available, SIP trunking is always preferred. If your provider is not listed above, it is likely still compatible as long as it supports standard SIP (RFC 3261) or unconditional call forwarding. Contact Kallin support if you need help confirming compatibility.

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Connecting via SIP Trunk

SIP trunking creates a direct, low-latency connection between your VoIP provider and Kallin. This is the preferred method for the best call quality and reliability.
1

Create a SIP trunk or outbound route in your VoIP provider dashboard

Log in to your VoIP provider’s admin portal and navigate to the section for SIP trunks, outbound routes, or carrier connections — the exact label varies by provider. Create a new trunk or route to represent the connection to Kallin.
2

Point the trunk to Kallin's SIP endpoint

Set the outbound proxy or SIP server address to the Kallin SIP endpoint shown in your Kallin dashboard under Numbers > SIP Settings. This address is unique to your account and should not be shared.
3

Add your number in Kallin

In your Kallin dashboard, go to Numbers > Add Number and select VoIP / SIP Trunk as the connection type.
4

Enter the number and SIP credentials

Enter your phone number in E.164 format (e.g. +442071234567). Then paste the SIP username, password, and domain provided by your VoIP provider into the corresponding fields in Kallin.
5

Save and run a test call

Click Save to activate the connection. Place a test call to the number from an external phone to confirm that calls are routing correctly into Kallin and that audio quality is acceptable in both directions.

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Connecting via Call Forwarding

If SIP trunking is not available on your current VoIP plan, you can connect using unconditional call forwarding instead.
1

Log in to your VoIP provider's dashboard

Navigate to the call forwarding or divert settings for the number you want to connect.
2

Generate a Kallin DID number

In Kallin, go to Numbers > Add Number > VoIP / SIP Trunk to generate a Kallin DID number — this is the number your VoIP provider will forward calls to.
3

Set up unconditional forwarding

Set an unconditional forward (sometimes called “always forward” or “divert all calls”) to the Kallin DID number.
4

Verify the connection

Save the setting in your provider’s dashboard, then place a test call to confirm calls are arriving in Kallin correctly.
SIP trunking is strongly preferred over call forwarding. A direct SIP connection reduces latency, avoids the audio re-encoding that can occur with forwarded calls, and gives Kallin full visibility of call metadata such as the original caller ID. Use forwarding only if your VoIP plan does not support SIP trunks.
Your SIP credentials — including the SIP username, password, and authentication realm — are sensitive. Treat them like a password: do not share them in emails, chat messages, or public forums. If you believe your SIP credentials have been compromised, regenerate them immediately from your VoIP provider’s dashboard and update the settings in Kallin.

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Next Steps

Virtual Numbers

Learn how Kallin’s virtual number system works and how it relates to your connected VoIP numbers.

Configure Call Routing

Build routing rules, time-based schedules, and call queues for your connected VoIP number.