May be this is a little late, but I just join the forum, and I seem like to have the same setup as your T-Mobile Dash+Total Internet Unlimited plan+Nokia 770. Seem like a perfect setup. Anyway, after I digg around, not related to the super popular website in anyway, I found some thing that could be a solution. Appearently, there are other n770 owner that have the same problem w/ T-Mobile SDA, understanding that it's not the same phone, but it's base on similar OS, WM5. And they seem to have a solution.
http://thoughtfix.blogspot.com/2006/...h-windows.html
If anyone still have the T-Mobile Dash, and like to try the setup, please post the result. I very would like to know.