Skip to main content
BT and Openreach geographic numbers — those beginning with 01 or 02 — are among the most common business and residential phone numbers in the UK. Kallin connects to these numbers directly, letting you layer intelligent call routing, voicemail, IVR menus, and call analytics on top of your existing line without disrupting your current service.

​
Prerequisites

Before connecting your BT or Openreach number, make sure you have the following ready:
  • An active BT or Openreach line — the number must be in service at your current provider
  • Account holder access — you must be the named account holder, or an authorised contact, to authorise any changes
  • Your CLI (Calling Line Identity) — this is the number presented when you make outbound calls, and it must match the number you are connecting to Kallin

​
Supported Number Types

Kallin supports the following BT and Openreach number types:
  • Geographic numbers — 01xxx and 02xxx numbers assigned to a specific location or area code
  • ISDN lines — ISDN2e and ISDN30 circuits with geographic CLI presentation
  • SIP trunks via Openreach — numbers provisioned over Openreach’s Ethernet and SIP infrastructure

​
Connecting Your Number

1

Log in to Kallin and go to Numbers > Add Number

From your Kallin dashboard, navigate to Numbers in the left-hand menu and click Add Number in the top-right corner.
2

Select BT / Openreach Landline

On the provider selection screen, choose BT / Openreach Landline from the list of connection types.
3

Enter your phone number in E.164 format

Type your number in full international format, starting with the UK country code. For example, a number with the area code 01234 would be entered as +441234567890. Do not include spaces or hyphens.
4

Complete the ownership verification

Kallin will verify that you control the number by placing a short verification call to it or sending an SMS with a one-time code. Answer the call or enter the code when prompted to confirm ownership.
5

Configure your routing rules

Once verified, your number appears in the Numbers section of your dashboard. Click the number to open its settings and configure call routing, voicemail, business hours, and any other options.

​
Forwarding vs Porting

When connecting a BT or Openreach number, you have two options for how calls reach Kallin: Call Forwarding keeps your number registered with BT and your existing line active. BT forwards incoming calls to a Kallin Direct Inward Dial (DID) number, and Kallin then applies your routing rules. This is the quickest way to get started and requires no disruption to your current service. Your BT contract and billing continue as normal. Number Porting moves your number fully to Kallin, so BT is no longer involved in the call path. Your BT line is cancelled as part of the process, and Kallin becomes your number’s host carrier. Porting removes any dependency on your old provider and typically results in lower per-call costs and simpler billing. See the Number Porting guide for full details.
BT is phasing out its ISDN network by January 2027 as part of the UK’s Public Switched Telephone Network (PSTN) switch-off. If you are currently using ISDN2e or ISDN30 lines, you should plan your migration to SIP before this deadline. Kallin’s SIP trunk connection is a direct replacement and supports all the same geographic number ranges.
If you are connecting your number via call forwarding, do not cancel your BT line — doing so will disconnect your number and break the forwarding route to Kallin. Only cancel your BT service after a full number port has been confirmed as complete by Kallin.

​
Next Steps

Port Your Number to Kallin

Move your BT number fully to Kallin and stop relying on BT forwarding.

Configure Call Routing

Set up routing rules, time-of-day schedules, and call queues for your connected number.