FYI:
http://wapreview.com/blog/?p=8077
"T-Mobile introduced a new Web Day Pass option for its prepaid users this week. It provides 24 hours of unlimited data access for $1.49. [...]T-Mobile mentions a 30 MB daily soft cap on the Terms and Conditions page that you click though when activating a DayPass. After 30 MB, download speed is supposed to be slowed. I tested that by downloading over 200 MB and I don't seem to have encountered the cap. Even after 200 MB I was getting speeds in the 300-500 kbit/s range. While that's slower than the best speed (1859 kbit/s) I saw, it's still 3G performance."

I got this working on the new APN, epc.tmobile.com , with the icon for network speed showing "3.5G". I don't know about others.