So pairing the ultrasim with your friend's sim card works in the iphone correct?
Are the contacts in identical positions for the two sim cards?
Are you mated correctly with the ultrasim and your sim?
does it insert the same as with your friend's or did you notice a difference.
Caution-if you try the sandpaper, be very very careful. I went slow and deliberate with a large grain sand paper just until it with the ultrasim were the same thickness as the included at&t sim. You are doing this at your own risk!
As a last resort, have you talked to your friend about buying your jailbroken I phone? :-)
Good luck and let us know!