On Tuesday I discovered (which resulted in lots of buzz) the new Sprint Android 4.2.1 Update that is still being staged as a OTA for Sprint Customers. Now you can wait for Sprint to roll the update out through a normal OTA or you can follow the steps below which do not require root or even a unlocked bootloader and since you’re not flashing a custom ROM but instead just sideloading a official update your warranty should stay intact.
Step One: POWER Phone Off
Step Two: Hold UP and DOWN VOLUME + POWER until you land in fastboot menu then use the up arrow to select “Recovery” and press POWER to confirm the choice. You will then be taken to a screen showing an android with a red exclamation mark on this screen press UP and DOWN VOLUME + POWER until your taken to the next menu where you will tap the DOWN VOLUME once and use POWER to select choose the option “apply update from adb.”
Step Three: Connect your Galaxy Nexus to your Ubuntu system via USB cable.
Step Four: In terminal run the following command without the quotes “wget http://android.clients.google.com/packages/ota/samsung_proxima_toroplus_sprint/c5ea6e959840.update_mysidspr_FH05_to_GA02.zip && adb sideload c5ea6e959840.update_mysidspr_FH05_to_GA02.zip”.
Now you should see progress in terminal and then after about 10 minutes your phone will complete the update procedure and you can use the volume control to select the reboot option. You should now have Android 4.2.1 on your Sprint Galaxy Nexus and to check just go to “About Phone” under Settings and it should look like this: