Excellent ... I recently signed a one-year contract for T-mobile WiFi service basically just to use in CRC's, so this is excellent news that I'll be able to use it at Hyatt hotels also.
In general, other locations that have T-mobile are Starbucks, Borders, and the AA Admirals Club.
Note that you can also get a nice deal for the first year usually, 10,000 bonus miles on AA, DL, or UA ... take a look at
this thread for discussion of the various promos available.