I recently got my 9800 and decided to use some instructions found online to enable UMA on it. A fair WARNING if you decide to do this you can seriously mess up your device if you do not follow step by step instructions or decide to mess with other options. The process does take some time specially if you do not have the necessary tools installed on your computer so make sure you have some time set aside before you decide to do this. Make sure to read the full instructions before you start the process. This is only for those that have a 9800 on T-mobile UMA does not work with AT&T.
The full instructions are found in the forums section of Berryreview, as well as credit to where the original instructions came from.