5.1 Updated Instrcutions:
With the SIM you want to use the the phone :
1. Put the phone into Airplane mode (I’m not sure this is needed, but it doesn’t hurt)
2. Go to Settings -> About Phone and tap on "Build Number" until it says you are in Developer Mode (~10 times)
3. Go back one menu, and right above About Phone there should now be an option for Developer Options, go into that.
4. Turn on USB Debugging
5. Connect the phone to your computer and type "adb shell" in your CMD window
6. Run the following commands in adb shell :
pm clear com.android.providers.telephony
settings put global preferred_network_mode 9
settings put global preferred_network_mode1 9
settings put global preferred_network_mode2 9
7. Turn off Airplane mode
8. Power off and Restart the phone
9. Open up the settings app, go to the mobile networks panel, select "Prefered Network Mode" and change it to "4G"
10. Input the appropriate APNs for your specific carrier