I now am a T-Mobile cell phone subscriber and I have it working with the high speed (56kbps) data on my cell new V300. It was a pretty smooth operation. Here are the important references:
http://www.taniwha.org.uk/
http://www.xochi.com/aircard/
The Robb Barkman page is the most important. Use the GPRS scripts.
I used the Motorola GPRS VID1 57k profile used the internet2.voicstream.com phone number, turned off PPP Echo Packets and turned on TCP header compression under PPP options.
I earlier tried to make a sierra card work and failed – the driver (both free and pay) was botched so I took it back.
Right now I am in San Diego and really getting 56Kbps. Tres cool.