Change Sim Card Number Galaxy S3
If you are referring to the "My Number" field then I answered the question here.


  The "My Number" isn't actually stored on the phone, it is stored on
  your sim card. Stock android can't edit this data. CyanogenMod can, so
  can iPhones and BlackBerrys. If you can get your hands on one of these
  then just pop your sim into it and edit the "My Number" field and Bobs
  your uncle.