This is about the strangest thing (or maybe it isn't?) Its a friends 3GS (no history before he acquired it from his cousin with a broken screen and updated it to ios5), its on ios5 and maintains a good signal unless you put it in your pocket...about 1 in 10 times you take the iphone out of your pocket and its showing No Sim. I've tried restoring as a new iPhone, changed sim card several times and even transferred the mainboard into a different 3GS chassis. Had 3G on and off and location services on and off. Googled for an answer but nothing seems to help. Now I'm lost for ideas...anyone help?