How to Divert Calls from Landline to Mobile UK: BT, Sky & VoIP Codes

Quick answer: To divert all calls from your landline to a mobile, pick up your landline handset and dial *21*[mobile number]#. You'll hear a confirmation tone. This code works on BT, Sky, TalkTalk and most other UK landline providers. To cancel the divert, dial #21#. However, with the UK's PSTN switch-off completing by January 2027, a cloud-hosted VoIP phone system offers a far more flexible and future-proof alternative to traditional call diversion.

How Do I Divert My BT Landline to a Mobile?

BT uses standard star codes for call diversion. Here's how to set it up step by step:

1. Pick up your BT landline handset and wait for a dial tone.
2. Dial *21* followed by your full mobile number, then press #. For example: *21*07700900123#
3. Listen for the confirmation tone — a short interrupted dial tone confirms the divert is active.
4. Replace the handset. All incoming calls will now forward to your mobile.
5. To cancel: Pick up the handset and dial #21#. You'll hear a confirmation tone.

Important: BT charges for diverted calls at the same rate as if you had made an outgoing call to that mobile number. This typically costs between 10.24p and 21.24p per minute depending on your BT calling plan. Calls are charged from the moment your mobile rings, not from when you answer.

We recommend: If you regularly divert BT landline calls to a mobile, check your BT call plan includes mobile minutes — otherwise costs can escalate quickly.

What Are the Call Divert Codes for Each UK Provider?

Note: The *21* code is a universal standard across most UK PSTN and digital voice landlines. If it doesn't work, contact your provider — some newer digital voice services manage diversion through an app or online account instead.

What's the Difference Between Divert All Calls and Divert on No Answer?

UK landline providers offer several types of call diversion:

• Divert All Calls (*21*) — Every incoming call is instantly forwarded to your mobile. Your landline phone won't ring at all.
• Divert on No Answer (*61*) — The landline rings for approximately 15–20 seconds first. If nobody picks up, the call is forwarded to your mobile.
• Divert When Busy (*67*) — Calls are only forwarded when the line is engaged.

Best for most businesses: Divert on No Answer (*61*) is usually the better choice for business use, as it lets you answer at the desk when you're there and catches calls on your mobile when you're away.

Why Is VoIP a Better Alternative to Landline Call Diversion?

Traditional call diversion works, but it's a blunt tool — especially for businesses. Here's why a cloud-hosted VoIP phone system is a smarter long-term solution:

• No per-minute diversion charges — calls route over the internet, so forwarding to mobiles, home phones or other offices is typically included in your plan.
• Simultaneous ring — ring your desk phone, mobile app and laptop at the same time, rather than sequentially.
• Time-based routing — automatically forward calls to different numbers based on time of day, day of the week, or bank holidays.
• Hunt groups and auto-attendant — route calls to teams, not just one mobile number.
• Keep your existing landline number — port your number to VoIP and it works exactly as before, with far more flexibility.
• PSTN switch-off ready — BT's Openreach is switching off the traditional phone network by January 2027. Star codes like *21* will stop working on legacy lines. VoIP is already future-proof.

Hosted VoIP phone systems for UK businesses typically start from £6–£15 per user per month, which often works out cheaper than paying ongoing diversion charges on a traditional line.

How Do I Set Up Call Forwarding on a VoIP System? (Step by Step)

If you've already moved to a hosted VoIP phone system, setting up call forwarding is done through your online admin portal rather than dialling star codes:

1. Log in to your VoIP admin portal or management app.
2. Navigate to call routing or call forwarding settings for your extension or phone number.
3. Choose your forwarding type: always forward, forward on no answer, forward when busy, or simultaneous ring.
4. Enter the destination number — this can be a UK mobile, another extension, an international number or a ring group.
5. Set optional rules: time-of-day schedules, voicemail fallback, or overflow to a colleague after a set number of rings.
6. Save and test by calling your number from another phone.

Our pick: For UK businesses with 2+ staff, a hosted VoIP system from Connection Technologies gives you enterprise-grade call routing without the complexity or cost of traditional PBX hardware.

What Happens to Landline Call Diversion After the PSTN Switch-Off?

Openreach is retiring the UK's Public Switched Telephone Network (PSTN) and ISDN by January 2027. After this date:

• Traditional analogue landlines will no longer function.
• Star divert codes (*21*, *61*, etc.) will stop working on legacy lines.
• All voice services will move to digital (VoIP) connections delivered over broadband.
• BT's "Digital Voice" service already replaces traditional landlines for residential customers — businesses need to plan their own migration.

We recommend: If your business still relies on traditional landline call diversion, now is the time to plan your move to VoIP. Leaving it until 2027 risks disruption and rushed decisions. Connection Technologies can manage the full migration, including porting your existing numbers.