Yep, I paid a lot of attention to your experience, lol... Actually I think you have noticed that someone has tried out that the device also encountered the same problem in UK, not reporting an invalid SIM card but just keeps on searching for signal.
BTW, have you traveled inside the US where is not covered by the Cricket's own network? They told me that iPhone would not be guaranteed to work when it's covered by their partners' network such as Spring or MetroPCS... Crossing my fingers, waiting for your answer! Thanks!