If you’re tired of waiting for the official RC29 update for your T-Mobile G1 to roll out, here's a way to do it right now, but manually. All you need is a PC, internet connection, a way to transfer the firmware to your Micro SD card and a brain.
Here's what you have to do:
1. Grab the RC29 update from Google here.
2. Rename it from signed-kila-ota-115247-prereq.TC4-RC19+RC28.zip to update.zip, and place it in the root of your Micro SD card.
3. Turn off your G1, then turn it back on by holding the Home+End keys until you see an icon popup after the T-Mobile G1 logo.
4. From the icon screen, open the keyboard and hit Alt+L. This will display the log saying what is happening (although you can skip this step).
5. Now press Alt+S to begin the update. Remember, the update needs to be in the root of the Micro SD card and needs to be named update.zip.
6. Once it finishes, just follow the onscreen instructions and press Home+Back to finish.
7. The G1 will reboot a few times to flash different parts of the firmware.
Congrats! Now you have the latest firmware version running on your device.
The info is taken from MobileCrunch.com.