No, Actually I am glad you posted this thread OP, it's good to know Fring allows Voip over 3G...not many people are aware of that. ( AT LEAST I WASN'T)
I originally HAD Fring ( I still do but not synced with my iphone currently) I replaced it with the Skype app, then went to Cydia and downloaded and installed voipover3G... It works great with the Skype app.
So basiclaly I don't think I will change anythign at this moment, but it's good to know this info, b/c for whatever odd reason I need to uninstall "voiceover3g" from Cydia or if I ever lose my Jailbreak, it's good to know Fring is a nice back-up option to continue using Skype over 3G (which I have been using lately a lot to talk to my friends and cousins in Europe)
thanks again OP 😉