This came across a mailing list I’m on:

Inside the iPhone field test mode – Blog – WirelessInfo.com

Basically if you dial:

*3001#12345#*

Then you get dumped into a menu which allows you to read out all sorts of interesting details about your phone and its connection to AT&T’s network. Note: I did this on my phone, it seems harmless enough, but don’t come crying to me if something bad happens.

Addendum: DOH! I inadvertently left out the 5 above when I first posted this.

[tags]iPhone,iPhone Field Test[/tags]