Should you be the sort of amateur engineer to whom cryptic numbers and codes are the spice of life (or if you just want to find out what firmware version your iPhone is running), then Field Test mode is the thing for you. Giving you information about which AT&T cell tower you’re connected to, your signal strength and EDGE status, it’s unlikely to be of interest to the average iPhone owner, but we know you guys hate to be average.
Dialling *3001#12345#* (as discovered by WirelessInfo) brings up the Field Test mode, and then you have a variety of options to go through and, if you’re anything like me, be confused by. Remember, although usually these testing modes are read-only, there’s always a possibility that you might inadvertently change something and render your beautiful handset into a brick. With that in mind, we’re offering this up for information value only; we don’t recommend you do it.
[via iPhoneHacks]
Interesting. Since the manual keypad is used for special purposes one time, it’s possible that unblocking an iPhone can also be done by entereting the right numbers here.