I did a search and I found a list of of Tmobile phones that are no longer for sell.... I did not know T mobile had a treo.
Discontinued T-Mobile phones
Cam did a pretty fun review of the original T-Mobile sidekick on tmonews:
Really goes to show how far we've come!
Retrieving data ...
Manage your T-Mobile account
Use the T-Mobile App or your My T-Mobile account
We're here to help