iPhone 4 users on T-Mobile may have noticed the loss of service / sim errors when rebooting the phone. The problem isn't ultrasn0w. For some reason, on iPhone 4's startup, 3G is enabled. iPhones on T-Mobile can't work with 3G so it gives you a crapload of errors and you may need to reboot the phone a couple of times just to get it working. If you can find out how to permanantly disable 3G on startup, your problems should be fixed. I don't know if this problem goes for everyone, but I've seen numerous threads about this problem without any fix. I haven't found out how to do this yet but I'd update the thread when I find something.