My3G is a useful tweak that makes apps believe that they are on WiFi instead of 3G. My3G was updated and now supports FaceTime calls. Yes, we can make FaceTime calls over 3G and not just WiFi as Apple/AT&T wants us to.
You can find My3G in Cydia and/or RockApp. If you install it via Cydia , it will still have RockApp dependency, which you can remove via SSH if it bothers you.