I’ve had a few people who only want to jailbreak their iPhone just so they could use FaceTime anywhere. Right now it only works on WiFi but with 3G Unrestrictor it will run on 3G and even EDGE. Every once in a while I would have problems keeping the call connected. It seemed, after about a minute, that the call would freeze and then disconnect randomly. It also seemed like it was happening with anyone and anywhere.
Well, I think I figured it out! Both of my grandparents have iPhone 4s and they live in 3G and have no WiFi so both are jailbroken and using 3G Unrestrictor while I also am jailbroken using 3G Unrestrictor. The difference for me was I was on WiFi during the calls. When I was talking with my grandpa tonight I decided I gotta figure this out! After about 5 calls, all 5 dropped around the 1 minute mark. Then I tried something crazy (sarcasm). Since I was on WiFi I thought I would try turning off 3G Unrestrictor. If you use SBSettings, you can just toggle it off before the call. Tada! I called both my grandma and grandpa again with FaceTime and had no drops!
So, the solution again. When jailbroken and have 3G Unrestrictor installed, toggle it off when making the call over WiFi. If you are still having troubles or have another fix, please let us know in the comments.