Where is my iPhone 3GS GSM module located?

And how can I tell if it should be replaced?

My iPhone was dropped and now it gets signal after about 5 minutes of leaving the sim card in. Then it goes up to 1, 2, and 3 bars then back to nothing. I've checked my Number 7 connection and changed the dock connector and I got the same thing! HELP!!! Pictures would be extra helpful!!!