We had a training at work today all about how the GSM phone system works. At the end, the speaker showed us how to find out all sorts of information about your GSM connection on an iPhone. You can see information about a call in progress, network information, which cell phone towers your phone can see, information about your GPRS (internet) connection, and what firmware version you are running.
One of the cool things about this is that you can see how walking around in a room, say, makes your connection to any given tower stronger or weaker.
If you have an iPhone, check it out. Dial *3001#12345#* then hit call.
And no, I don't have an iPhone. The company has a few for testing our apps, so we got to play with those. My current phone is a Nokia N80.