Looking to port a mobile number instead? View the Mobile Porting Guide here.
To transfer your existing landline number to ONSIM, please email the following two documents to support@onsim.uk:
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A Completed Porting Form: (Attached at the bottom of this article). This must be fully completed, signed, and dated. For a step by step guide on how to do this please click here.
Tip: We strongly recommend asking your current provider for your "Porting Information" to ensure the details on this form are 100% accurate.
Your Latest Invoice: A copy of your most recent bill from your current provider, showing your name and the registered address they hold for you.
Important: We cover the cost of your first single-line port. However, if a port fails due to incorrect information, we reserve the right to pass on the charges for subsequent submissions.
Key Requirements for a Successful Port
Keep Your Service Active: Do not cancel your service with your current provider yet. If the line is disconnected before the port completes, you may lose the number permanently.
Active OnSIM Service: You must have an active ONSIM account before we can start.
Temporary Number & Caller ID: We will provide a temporary number during the process. Once we receive your form, we can set your outgoing Caller ID to show your porting landline number immediately.
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Incoming Calls: If you want to receive calls on your ONSIM SIM before the port is finished, ask your current provider to forward calls to your new temporary ONSIM number.
Important: Broadband on the Same Line
If your broadband service is linked to the landline number you are porting, the port will likely cancel your internet. To prevent this, you must contact your current provider and ask them to "renumber the broadband." This moves your internet service to a different number, keeping your landline active and available for porting.
Porting FAQs
| Question | Answer |
|---|---|
| How long does it take? | On average, 10–14 working days after we receive your documents. Times can vary based on your current provider. |
| What is a CUPID/Underlying Carrier? | This is the company that "owns" the number range (e.g. BT, TalkTalk, Gamma). Your provider (e.g. Sky) might be different from the underlying carrier. |
| Will I be charged? | We cover the first single-line port for our SIM plans. If you are porting a number into our virtual landline service there is a one of fee of £20 + VAT. You are responsible for any fees from your old provider, failed port fees (due to incorrect info), or cancellation fees. See our Non-Standard Charges for details. |
| Why pay for two services? | You need an active "destination" (ONSIM) and an active "source" (current provider) for the transfer to move through the network. |
| Can they refuse my port? | Under Ofcom regulations, providers cannot block you from porting your number. If you face resistance, contact us immediately. |
Next Steps
Download the Porting Form below.
Confirm your details with your current provider.
Email your form and latest bill to support@onsim.uk.