I guess the proximity sensor for the iPhone 4S is different than the i4. I talked to the Otterbox manufacture and they said that a i4 case blocks the sensor to the i4S. You can still use the case but the screen on your phone will not go off when close to your face. She did say however the new case for i4S will work with an old i4 with no problems. Just some useless knowledge for anybody thinking of using their old Otterbox case for the i4S. Time to spend $50 for the new i4S case. It's worth it though IMO.