I use it with a Sony Ericsson W810i Quad band phone. The phone was purchased in Germany at T-Mobile Germany and unlocked there. I now use it with a T-Mobile USA Sim card and T-Mobile USA contract. I get solid 240kbps (~25kb/s) in most places. Bluetooth (Linux PC, Palm, N810) and USB (Linux PC) work great on this phone.

Martin

Edit: I am grandfathered into their old Unlimited Data plan for 20USD/month (add on to existing voice plan). I don't think they still have an unlimited data plan that allows for tethering for 20USD/month.