Every phone has a secret vocabulary, codes that you can type into the number pad that produce backdoor access to phone information. To use these codes, open the Phone application, and tap Keypad. Next, enter the codes exactly as stated, including any stars and pound signs. Tap Call after entering the code. The iPhone implements a large subset of the standard GSM service codes as well as a number of AT&T-specific ones. Here are is sampling of the codes you can use on your iPhone. To learn more, Google for GSM codes.
Basic iPhone Information
Use these shortcuts to view information about your iPhones core functionality:
*3001#12345#*: Enter Field mode. Field mode reveals many of the inner settings of your iPhone, specifically up-to-date network and cell information.
*#06#: Displays your iPhone IMEI, the unique identifier for your cell phone hardware. (No need to tap Call.) Together with your SIM information, it identifies you to the provider network.
Service Shortcuts
These shortcuts provide quick access to information about your account:
*225#: Bill balance. (Postpaid service only; the acronym is BAL for balance.)
*777#: Review account balance for prepaid iPhones on the GoPhone plan.
*646#: Check remaining minutes. (Postpaid service only; the acronym is MIN for minutes.)
*3282#: Check your data usage. (Postpaid service only; the acronym is DATA.)
*729: Make a payment. (The acronym is PAY.)
611: Connect to customer service.