iphone 4s drops signal on T-Mobile USA

Hello everyone.

I am currently using tmobile (USA) in a factory unlocked iphone 4s and would like to know if anyone has issues with the reception.

Here's the problem that bugs the heck out of me:

Prior to making a phone call...I have 5 bars of reception. Once I make the phone call, the edge icon disappears but the bars remain (normal that it disappears when phone call is placed right? ) Throughout the phone call, everything is gravy...no dropped calls and clear as the current windy skies...however, as soon as I end the call, the reception drops and the phone goes into a search mode...about 15-30 seconds later, the reception recovers from 1 to 2 to 3 to 4 to 5 and then the edge icon appears. This process occurs everything single time I end a call. Does anyone have any insight as to why this occurs. Its rather annoying.

I also went to apple store and explain the problem but thay say that u have change the sim and i call t mobile and change my sim but the problem sill exits at the apple store the restore my iphone three time but sill same problem and the even told me that don't restore from backup but same problem so if any one als have this problem plz help me what to do ...

Thanks in advance!