GSM information

Since the iPhone is a GSM (Global System for Mobile communications) phone, you potentially have access to numerous codes that can be entered on your phone's keypad to either give you information about your phone (like your IMEI) or to activate or deactivate features (like call forwarding, barring and SMS delivery reports to name a few).

Here's a sample of some of the codes you can try.

*#06# - Displays your International Mobile Equipment Identity (or IMEI for short). The IMEI number is used by the GSM network to identify valid devices and therefore can be used to stop a stolen phone from accessing the network.

*#21# and press Call. Settings for call forwarding for calls, data, fax and sms.

*#30# and press Call. Calling line presentation check.

*31# (followed by the number you are dialing) - Sets outgoing "Caller ID" to be private.

#31# (followed by the number you are dialing) - Sets outgoing "Caller ID" to be visible.

*#31# (followed by the number you are dialing) - Displays current setting of outgoing "Caller ID". (Disabled = visible, Enabled = private).

*#33# and press Call. Check for call all barring.

*#43# and press Call. Determine if call waiting is enabled.

*#61# and press Call. Check the number for unanswered calls. Shows the number for voice call forwarding when a call is unanswered. Also shows the options for data, fax, sms, sync, async, packet access and pad access.

*#76# and press Call. Check whether the connected line presentation is enabled or not.

*225# and press Call. Bill balance for postpaid accounts only.

*646# and press Call. Check the minutes for a postpaid account only.

*777# and press Call. Check the account balance for a prepaid iPhone.

If you'd like an easy method of using these codes, then download this vCard and import it into your address book, then sync the address book with iTunes. It will then add these codes as contacts in a group labeled "123" at the end of your address book list. You can then merely pick the on you want and press it to activate it and not have to enter a code.

Here are some sites that list some more of these codes:
I know the GSM codes are impossible to remember, so a reader (thanks Foob!) whipped up this pocket guide (and a handy to do list and calendar to boot) that you could bring with you to jog your memory.

Here's a blog on how this pocket guide is made, with plenty of images to show you how to fold it up. PagePacker makes pocket-sized books.

Field Test menu

The Field Test menu is used to view various engineering parameters, such as signal strength, frequency band, tower ID, et cetera. This is a menu that lets you look at the inner workings of the iPhone from a telephone technician's view. The great majority of iPhone users will never need access to this menu.

You get to this menu by entering *3001#12345#* and press Call. Here are some of the screens you'll have access to:

iPhone       iPhone

iPhone       iPhone

To exit the Field Test menu push the home button.

Previously, the screen labeled "Cell information" contained information regarding cell phone towers in your area, your signal strength to those particular towers, and what band your iPhone is running in (among other things). This information doesn't seem accessible in 3.0 firmware. But for more information about interpreting the data found here, see this site.

For even more information about the technical side of field test menu check out this site, and this site.

Return to top of page