As I mentioned in an earlier post, my online exchanges with T-Mobile support imply that T-Mobile does not object to my tethering my G-1, although they don't support it. I'm not sure if that's really the corporate view of the matter, but having been told so by two levels of their tech support I think I am entitled to try it.
So I did. The first step is to get root access, taking advantage of a bug in the original version of the OS. I successfully downgraded my OS to the original version (CR29), and I believe I got root access--at least, the attention symbol in the Terminal window is # rather than $.
I have been unable, however, either to make Android-WiFi-Tether work under CR29 or to install the upgrade that is supposed to take the OS back up to a more recent version while preserving root access.
Is there any kind soul among my readers with suitable expertise who would like to advise?