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:

  1. Launch the phone dialing app
  2. Type this phone number
    ##7820
  3. Press “Call”
  4. You should be prompted to enter the unlock code at this point (it will take a few seconds to load)
  5. Type in the unlock code you received from your provider
  6. Tap the “Check” to submit
  7. Wait a few seconds – the icon will change to “unlocked”

lumia_SIM_unlock

If you have a foreign SIM available, here’s the steps you can use:

  1. Power the phone OFF
  2. Remove the battery and insert the SIM from another carrier
  3. Enter the SIMcard PIN if it is necessary
  4. The phone will ask for a SIM unlock code.
  5. Input the code received above
  6. Tap the “Check” to submit
  7. You will have 10 tries to enter the code correctly
  8. Wait a few seconds – the icon will change to “unlocked”