Best answer by Mohammed
Welcome to the iD Community.
You will continue to be billed your normal line rental once the contract expires.
What you can do is head into the iD app or on MyiD and follow the options to upgrade to a SIM-Only plan.
This will then convert you over to a SIM-only plan at your chosen tariff.
Everything will happen automatically so you don't need to do anything else and you'll keep the number and billing date the same etc.
Hope this helps!