The new EDGE services from AT&T look pretty promising. I got a demo of the Sony-Ericsson solution (a PCMCIA card silimar to the Sierra Card from T-Mobile) and I was really impressed.
Read more about EDGE here.
The speeds are supposed to be be around 200Kbps burst and an average of around 120Kbps. It was definintely faster than using my T610 over the GPRS network via Bluetooth. The other nice thing about EDGE is that it's being offered on certain handsets as well. Here are the EDGE-compatible devices (2 Nokia handsets and a PCMCIA Card).
Might be the future!