If you do lock your BT One Phone SIM card, you'll need your PUK code, which you can find on the BT One Phone Portal in the Personal info tab under My Subscriptions. Then put the code into your phone to unlock your SIM.
Important: BT One Phone is no longer available to new customers. If you're an existing BT One Phone customer, you can continue using the service while we support you through its closure. If you're looking for a new communications solution, explore our BT Business Mobile and BT Digital Voice for Business options.