Lets do some digging....... Read everything before jumping in, just trying to help. But if you don't get yourself up to date on how things work, jump right in after each thing you read, and brick your phone, IT'S NOT MY FAULT! No piracy, no warez, no theivery allowed! Right terms in search will find what you are looking for.
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Garminfone - xda-developers
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Garminfone full hard root Achieved - xda-developers
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ASUSTeK Computer Inc.-Forum- A50 (Garminfone)
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Rooting Garminfone? YES ! - T-Mobile Community
If you find what you are looking for then congrats. But the sorts i read is if you want root, 2.xx and tether, find a diff phone. If you want to stay tmo then chehk out their lineup and search each device before you go out and get device your budy tells you to get.