It's the small (roughly 2cm by 1cm) microchip card that you insert into a phone when it's first set up. It provides the identity of a phone for the mobile network, so it can recognise, bill and send calls to individual customers. The Sim card is usually located behind the battery on the back of the phone.
Simply Key *#06# to find your "IMEI" needed for unlocking, this may also be found on the battery of your phone.
*Dial 0906 575 0302
And type your “IMEI’ code to obtain your unlock code.
Enter the instantly generated code and your mobile phone/cellular will be unlocked!!
*Calls charged at £1.50 per minute from BT landlines at all times. Calls from mobiles may vary. Over 18s only. Get bill payers permission. Please read terms of service before your call - Unlock your Mobile Phone.