i had the same problem on my 3gs, someone can help me?

the problem wasnt on flex cable, i think that is something on my motherboard broken

I had the same problem a couple of days ago. Went to AT&T and then Apple and they both told me that it couldn't be fixed. Apple guy even went as far as saying that I really wouldn't want to replace a 2 year old phone and might just be better to get an upgrade through AT&T. I did a little searching online and found this site and sure enough, the antenna connection had come loose. Popped it back in and got a working phone again.

Shame on apple for not actually wanting to service their products.