CricKet data should work (at least the connection part; not sure about the proxy), but I'm not sure what is involved in getting it up and running. You could attempt some of the tricks from
the TP2 USCC thread -- I think there's more hard information there than there is here.
Ringtones work, but if you've got some weirdly named files on your sd card, they can kill the media scan process before it finds them. (Solution: Clear off the files; then grab sdrescan from the market, or make a fresh data.img)
I think the fix is more accurately mj41374's. hamagc is responsible for some other fixes.