Withholding your telephone number means that it won't be available to the person you're calling. You can hide your number when calling from your BT landline or mobile.
To withhold your number on individual calls, dial 141 before the telephone number you want to call
To permanently hide your number, set it up in My BT online or contact us on 0800 800 150 to add or remove this service.
Both services are free of charge.