I have a 3gs 3.13 jb with spirit sitting on my desk with 5 full bars of signal. I have a 3gs 4.0.1 jb with jailbreakme.modmyi.com sitting on my desk that I just got from apple today with 3 bars of signal. I am not dropping calls and I dont think it has anything to do with the JB because I was like that before I did it. I think it has to do with the 4.0.1 software..... and yes I have even traded places where the phones are sitting as to be fair and no change. and both are black and 16gig just to let you know I am testing the exact same thing!!