I have Avantgo on my BB 7290 on TMO using BES. I don't know if t-zone browser works with avantgo. I also used it on a 7230 on TMO using BES. It worked via the Blackberry browser. Have you tried to connect to rim.avantgo.com manually using miniopra or Blackberry browser? It is strange that you cannot change your default browser to the blackberry browser and is stuck on t-zone.