Wil Limoges shares some of the iPhone codes that you can input on the number pad to perform a variety of tasks.
You may or may not be aware of it, but your iPhone has some secrets it's been hiding from you, some of which are handy, some of which are hacky. Your iPhone has the ability to accept codes that can be typed into the phone application, each of which can do different things. I’m going to explain how to access these codes and what they do. Most of the codes I’m going to share with you can be found on your carrier's website.UPDATE: The codes I supply below are specific to ATT. You can find the list of codes for Verizon on a couple of support pages:
You can also try this list for Sprint.
Let me describe how the codes work. First, open your Phone application. Once you’re in your Phone application, simply enter the codes by typing on the number pad and in most cases, you’ll just press call.
Upgrade your handset
*936# and press call
This is one of the most popular of codes. Entering this code will provide you with a text message that lets you know when you're eligible for a new phone upgrade.
Check your bill balance
*777# and press call
This will display your current bill balance.
Check your minutes
*646# and press call
This code will display your available minutes.
*#06# No need to press call
It’s probably not often that you need to retrieve your IMEI number, but in the event that you do, save yourself some time by using this code.
Interrogation settings for call forwards
*#21# and press call
Shows you whether you have voice, data, fax, sync, async, packet access, and pad access call forwarding enabled or not.
*#43# and press call
Tells you whether or not call waiting is enabled.
*3001#12345#* and press call
This one is my favorite. After pressing call, you’ll be granted access to the Field Test app. Aside from the technical info that you’ll see here, you can also enable the ability to display a cellular reception number instead of bars. The number represents how weak or strong your signal is. The higher the number, such as -100, the weaker the signal. The lower the number, -60, for instance, the better the signal. What’s even better is that you can replace those bars permanently just as I have on my own iPhone. While in the Field Test app, tapping the area in the top left corner of the screen will switch the setting between bars and numbers. Once it’s set to numbers, hold the Sleep/Wake button until the iPhone displays the slide to power off screen. Do not power it off. Instead, hold down the home button until the power off screen disappears. Now you have numbers permanently. To switch back to bars, simply repeat the process, only with bars enabled instead of numbers.