For quick access to troubleshooting, settings, or information about your cell phone bill, your iPhone supports some common call codes. We introduce some of the most helpful codes to you.
We informed you last fall about Apple’s iPhone Signal Strength Placebo, a code for the iPhone that aids in the identification of 3G network connectivity issues with AT&T.
Your iPhone does a field test when you enter *3001#123456#* and tap “Call,” and the results might be used, for example, to determine signal strength. (It also provides a ton of additional information that, unless you happen to be a cellular engineer, is probably beyond your comprehension.)
While the above code above is the iPhone’s most useful, there are a number of other interesting codes.
What happens if I type *# 21?
Call forwarding status for voice, data, fax, SMS, sync, async, packet access, and pad access is displayed by dialing *#21# and pressing Call. Keep an eye on this page for more updates on any code you want.