from Walt Mossberg at ReCode from ubersignal.com Replace your phones signal bars with numbers

http://www.ubersignal.com/field-test-mode

Go to the phone program of your iPhone, dial *3001#12345#*, hit send, you will go into field mode. It will show you the phones signal strength in numbers. I saved the number in my phone directory under phone signal strength so I can check the signal in numbers easily.