You can make 3G Unrestrictor work with 4.1 (I'm working off an i4, GP'd w/ iOS 4.1)...
1 Go into the 3G Unrestrictor settings and add "MobilePhone (FaceTime)" as an unrestricted app
2 Click the blue arrow to edit settings and TURN ON "Enable IsDirect Flag"
3 Leave WiFi on, it doesn't have to connect to a network, just needs to be on.
This is a workaround that has been posted until the 3G Unr. dev can update the app to work with 4.1, this works for now but can be a pain (especially in college campuses and other areas with widespread wifi blanketing [that doesn't have enough of a signal to transmit on but the phone still autojoins the network])