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Before beginning this process, you need to be aware that if the process is not followed precisely, the results can be a "bricked" phone. A bricked phone is one that will not boot and is, in fact, only useful as a brick. Missing a step in these instructions or inadvertently copying a corrupt installation file can sometimes result in a phone not booting properly. Re-downloading a component and attempting the component installation usually solves the problem and returns the phone to operation
This guide is for T-Mobile G1 telephones sold in the U.S.. This procedure has not been tested with any other Android based phone, and may not work with other phones. If you need help, the XDA Developer's Forum may be a good place to start.
Please read through all three sections of this how-to before beginning. This will give you an overall sense of what is required to complete this process.
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Before You Begin
There are a couple of things that you need to do before you begin this process. First, make sure your battery is charged. Having your battery go dead in the middle of a system update is a sure way to make your phone inoperable. This process will require you to completely re-format your memory card. Back up your memory card before starting the process if you have data that you would like to keep.
If the process goes smoothly, all three parts will take about two hours from start to finish. However, set aside at least three hours to allow for missteps.
Always download the required components to your computer and copy them to your SD card. A Micro SD reader is very helpful in Part 3 of this how-to. It will also make the overall upgrade process go more quickly.
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This process will completely remove all existing data and files from your phone. You will need to re-install all non-default apps and will have to copy all data back to your SD card.
This process will prevent T-Mobile from applying updates to your phone. You will have to watch the update list for the mod or ROM you install and manually apply any patches.
If T-Mobile is aware that your phone has been modified, they may decline to offer technical support.
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Downgrade Your Radio & System
- Backup your SD card. If possible, use a card reader to connect the SD card to your computer.
- Format your memory card as FAT 32. This is much faster if your SD card is in a card reader. An 8GB card can take up to 30 minutes to format in the phone. It takes around a minute in a card reader.
- Download DREAIMG.nbh. Android-DL.com is a good source, but you can also do a Google search.
- Copy DREAIMG.nbh to your memory card using your card reader.
- Turn off your G1 and insert the SD card.
- Hold the Camera Button down and press the Power Button to enter boot loader mode.
- Press the Power Button to start the upgrade procedure.
- When the update is finished, press the trackball.
- Perform a soft reset by pressing Call + Menu + End to reboot.
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Verify the Downgrade
When building a modified G1, it is very important to verify that each step has been executed properly. One you have installed DREAIMG.nbg, your phone should be running Android 1.0 and using RC29 for its radio. To verify the installation, do the following:
Once you have verified the downgrade, go to the next part in this series.
- Reboot your phone, if you haven't already, and enter your Google account information.
- When the phone powers up to the home screen, press the Menu button.
- Go to Settings.
- Scroll to the bottom and select About Phone.
- Look at the last entry, if the Build Number contains RC29, the downgrade was successful.
Rooting Your Android Based T-Mobile G1: Part 1, Downgrading Your Radio
Rooting your G1 and installing a modified ROM, like those from Cyanogen, Jesusfreke or Haykuro, will enable many features not included in the native T-Mobile build. A rooted phone also gives you access to a number of applications, like screen capture apps.