If you have received a replacement physical SIM card (for example, to replace a lost, damaged, or faulty card), follow the steps below to move your existing service to the new SIM.
Note: This guide is for replacement SIMs only. If you are activating a SIM for a brand-new service, please refer to our [Physical SIM Activation Guide] instead.
Step-by-Step Replacement Process
Because a replacement involves moving an existing phone number and data plan to a new piece of hardware, our team handles this manually to ensure a seamless transition.
Locate your SIM ID: Find the last 6 digits printed on the back of your new replacement SIM card.
Contact Support: Email our team at support@onsim.uk with the following details:
The SIM ID: Provide the last 6 digits (or simply attach a clear photo of the back of the SIM).
Service Details: If you manage multiple lines with us, please specify which mobile or landline number this replacement is for.
Wait for Confirmation: Our team will manually switch your service over. You will receive a confirmation email as soon as the swap is complete.
✅ Post-Activation Checklist
Once you receive the confirmation email that your replacement is active:
[ ] Insert the SIM: Place the new SIM into your device.
[ ] Reboot Your Device: This is essential to help the new SIM register with the network for the first time.
[ ] Check Your Settings: Ensure VoLTE (4G Calling) and Wi-Fi Calling are still toggled ON in your phone's settings.
[ ] Verify Data: If your plan includes data, check that your internet is working. If not, refer to our [Data Settings Guide].
A full guide on how to do this can be found here.
⚠️ Important Note
As soon as the replacement process is finished, your old SIM card will be permanently deactivated. You can safely snap and dispose of the old card once we have confirmed it has been swapped.