You will need to get a device unlock code from a mobile provider before using this guide. They are pretty cheap on the web, and free from AT&T at https://www.att.com/deviceunlock. If you purchased a GoPhone, and currently have an AT&T post-paid account, you need to use the “Non-AT&T Mobility Customer” option.
It was very difficult to find any information about how you can actually use this unlock code when you don’t have a different provider’s SIM card on hand. All guides I found required you to turn off the phone, swap a foreign SIM in, reboot, enter code…etc (see below). This method allows you to enter the unlock code without a foreign SIM and without turning the phone off.
A typical use case for this would be before going on a trip, where you plan to buy a foreign SIM card at your destination, but want to make sure your phone is unlocked and ready before leaving.
The steps are simple:
- Launch the phone dialing app
 - Type this phone number
##7820
 - Press “Call”
 - You should be prompted to enter the unlock code at this point (it will take a few seconds to load)
 - Type in the unlock code you received from your provider
 - Tap the “Check” to submit
 - Wait a few seconds – the icon will change to “unlocked”
 
If you have a foreign SIM available, here’s the steps you can use:
- Power the phone OFF
 - Remove the battery and insert the SIM from another carrier
 - Enter the SIMcard PIN if it is necessary
 - The phone will ask for a SIM unlock code.
 - Input the code received above
 - Tap the “Check” to submit
 - You will have 10 tries to enter the code correctly
 - Wait a few seconds – the icon will change to “unlocked”
 
		