I'm not sure I understand correctly, but my BB media setting was set to automatically mount when connected, so I changed that setting to "no". I don't have the problem with the file browser appearing any more, but the connection still dies after about 30 seconds.
I've tried ping and tracepath to rule out a dns issue, and neither work past that point, so the connection is definitely dying. I think it must be either a setting on my BB, or something wrong with the chatscript.
All I've done on the chat script is change the barry-tmobileus script to add in the IP and the other thing (ARP?) that T-Mobile gave me.
I did think looking at all the chatscripts that are posted online that I could get away with removing the IP and leaving it as "IP" - funny, I still get connected that way, but have no dns, so I guess the IP they gave me is for the primary dns server.