Originally Posted by toastido
I noticed on the TMO version of the GN3, that we are very limited in our service mode options. Well, I'm proud to say I've managed to get to the ACTUAL main menu of the service mode, rather than the debug info only menu.
*** DO THESE STEPS AT YOUR OWN RISK. I AM NOT RESPONSIBLE IF YOU BRICK YOUR DEVICE.***
Here's the trick I used on 4.4.2 Stock:
1) Open Phone, go to the dialer.
2) Enter *#197328640# to enter the service mode. You will land at "DEBUG SCREEN"
3) Hit the menu key, select "Key Input" and in the Input Value box, enter Q (capital letter) and hit OK
4) Hit the menu key again, select "Key Input", and in the Input value box, enter 0000 (four zeros) and hit OK
5) Wait about 5-10 seconds, your service menu should change to "MAIN MENU":
 PROTOCOL STATE
 UE SETTINGS & INFO
 DEBUG SCREEN(OPEN)
Now I haven't messed around in here too much, but if you want to reset your modem and GPS (restore the factory NV values for the modem, which COULD help data dropouts, bad GPS fix, etc.), do the following:
1) Enter the MAIN MENU as described above
2) Select option 2 "UE SETTINGS & INFO"
3) Select option 1 "SETTING"
4) Select option 2 "SYSTEM"
5) Select option 3 "NV REBUILD"
6) Select option 3 "ALL"
7) It will tell you to reboot. Do it. Reboot will take slightly longer, but it will completely reset the modem, GPS, and IMS settings
I'm sure there's a lot more that can be done that would be useful in the main menu, but I'm not feeling like destroying my phone ATTM, so I'll let others chime in.
Hit Thanks if you found this useful!