How To : Downgrade or Upgrade the firmware (RC) version on T-Mobile G1

There are many occasions when one needs to downgrade/upgrade the firmware version on his/her T-Mobile G1. For example, to get root access on your G1, you need to have RC 29 (for the US version) or RC 7(for the UK version). But, if you have a device with a higher firmware, you need to downgrade to RC 29 or RC 7.

Here are the steps that you need to follow. But, perform these steps at YOUR OWN RISK, because if something goes wrong, your phone can be bricked forever.

  1. Use a micro SD card, that has been formatted with FAT 32 mode.
  2. Download the firmware version you wish to install. Rename the downloaded zip file to update.zip. Place the file in the root folder of your micro SD card, and put the card in your device.
  3. Turn the device power off.
  4. Keep the Home+End button pressed until you see the T-Mobile G1 logo.
  5. Now, press Alt+L on your keyboard.
  6. Now, press Alt+S to begin the update process on your device.
  7. Carefully follow the instructions on your screen. Then, press Home+Backspace button to finish the process.
  8. Your device will reboot a few times, to completely flash your device with the new firmware.

To check, if your new firmware has been flashed, go to Menu > Settings > About Phone. Scroll down to the Build Number. If it reads the firmware you just flashed, then the update has been performed correctly.