The subscriber identity module, or SIM, card is the small card in your mobile phone that provides the phone with its network ID. It is the SIM card that allows phones to be locked and unlocked for individual use and provides the network service provider with the information necessary to allow the phone to function on a network. If your phone or SIM card has been damaged or is malfunctioning, it may be necessary to retrieve the SIM card's number before support representatives can assist you in fixing the problem.
Replace the SIM card as you found it. Take care to replace the card facing the same way as you found it, using the small indented corner as a guide. If you are replacing the SIM card correctly you will not have to force the card. Replace the battery in the same way as you found it, ensuring the metal contacts are set flush with the phone's contact points. Again, the battery should fit comfortably when it has been placed correctly. Replace your mobile phone's battery cover. It is now safe to turn on the phone.
If you are using an Apple iPhone, find the SIM card by pressing a paper clip gently into the small hole at the base of the phone and opening the SIM drawer. When you have retrieved the number, replace the SIM card in this drawer and push the drawer until it clicks.