I've got ultrasn0w on my iPhone 4 (4.1, baseband 01.59.00). Now when it works, it works well, I get about 4 bars in my room, brill. But then, for hours on end I'll end up with "No Service". I put the sim in another phone, it's fine, so it's not a signal issue, but then back in the iPhone, no service still. I've tried rebooting, powering off, no difference.
I go to carrier list, I can see the carrier in there, select it, but still no service.