Just wanted to tune in here and report that Ive been using virgin sim for a solid 2 weeks and have not had any interruptions in service or edge data. Works with all firmwares and modem firmwares so far. Best of all it does not require any modification or cutting of your original sim. But it does require your phone to be either activated with a att sim or with pwnage.
The only other sim adapter Ive tried before was universal sim V550, and that lost signal constantly which required a reboot to regain(especially edge, which happened daily). Finally got the No SIM card installed, message, which makes the sim unusable until you install it back into a tmobile phone... did this more than once too.
Point is, universal sim seems to be the most popular one on the market right now, and according to my experience the virgin sim blows it out of the water! After weeks of beta testing, they finally have decided to start selling a finished product online(I think only ebay right now or you can write the virgin sim rep at
virginsim@gmail.com and tell him I sent you.) There are two versions, normal speed and high speed, but as of now the normal speed is the only one being sold...as the high speed seems to have problems working with newer sim cards... when this problem is solved, it will be released to the public as well.
There is an ongoing thread on hackintosh if your interested in reading more on this product
Virginsim will be a good solution? - Hackint0sh