Nexus 7
Along with the Wi-Fi version Google has released Android 4.2.1 update for 3G version of Nexus 7. Google

Google has released the Android 4.2.1 (JOP40D) Jelly Bean over-the-air (OTA) update for the 3G version of the Nexus 7. The latest build has only bug fixes to problems found in the previous build.

To manually install the Android 4.2.1 update to the 3G Nexus 7, follow this tutorial. IBTimes UK reminds its readers it will not be responsible for any damage to the device during installation. Users are advised to ensure the Nexus 7 is updated to Android 4.2 (JOP40C) before following this procedure. Also remember to ensure the tablet is not rooted. This guide is meant only for the 3G version of the Nexus 7. Ensure all important data on the device has been backed up and the battery has at least an 80 percent charge.

To Install Android 4.2.1 (JOP40D) on 3G Nexus 7

    • Ensure appropriate drivers for the Nexus 7 have been installed (install Android SDK to install drivers)
    • Download Android 4.2.1 (JOP40D) (65880f56b1c0.signed-nakasig-JOP40D-from-JOP40C.65880f56.zip)
    • Download Fastboot (Fastboot.zip), which includes adb files needed to flash update
    • Extract Fastboot.zip, in computer, to access Fastboot folder with four files
    • Copy downloaded Jelly Bean firmware to Fastboot folder
    • Switch off tablet and boot into stock recovery (to do so, first boot into Bootloader by pressing Volume Down and Power buttons until screen turns on and then use Volume button to scroll to Start to change to Recovery Mode. Select using Power to boot into Recovery)
    • After an Android with a red exclamation point appears, hold Power and press Volume Up to see Recovery menu (try pressing both buttons together if above does not work)
    • Use Volume keys to scroll to and select Apply Update from adb option in Recovery by pressing Power
    • Connect tablet to computer and wait for drivers to finish installation
    • Click on Start in compute and follow this path: All Programmes > Accessories and right-click on Command Prompt and click on Run as Administrator
        • Note: If using Windows 8, this can be done by right-clicking on bottom left corner of the taskbar and selecting Command Prompt (admin))
    • Perform following steps in Command Prompt to flash Jelly Bean update
        • Navigate to Fastboot folder (if Fastboot folder is in C: enter cd C:Fastboot in Command Prompt and press Enter)
        • Type - adb devices. If device has been detected, a device ID will display in the Command Prompt. If nothing happens, ensure drivers have been installed
    • To install update, enter below command
        • adb sideload *filename* (replace *filename* with the name of the update file, including the .zip file at the end of the string)
    • After entering command, a message reading - sending: sideload - should appear and once that reaches 100 percent, installation will begin
    • After installation, select Reboot System Now from main Recovery menu

The Android 4.2.1 (JOP40D) update is now installed and running on the 3G Nexus 7. This can be verified by navigating to Settings > About Tablet.

[Source: Android Soul]