MobileSubstrate library that tricks apps into thinking that they are on Wifi even though they are on 3G/edge/grps. In the default config only Fring and AppStore are tricked. This way you can VoIP with Fring on 3G and download big apps with AppStore, even though Apple forbids it.
VoIPover3G is here to bring you just that, VoIP over 3G, or EDGE using the popular App Store app Fring, or Truphone. Along with allowing VoIP over the cellular network, it also will allow you to install App Store apps larger than 10mb, over the cell network It achieves this by tricking the apps into thinking you’re on a wifi network.
After install, by default, only Fring, Truphone, the iTunes Store, and the App Store are going to be tricked into thinking they’re on wifi. You can configure which apps get tricked by editing /Library/MobileSubstrate/DynamicLibraries/VoIPover3G.plist and adding the appâ€™s bundle identifier to that list. Removing VoIPover3G.plist will then make ALL apps be tricked, which isn’t recommended.
I was able to successfully able to use Fring and download an app over 10 MB over EDGE with AT&T. Not being on an iPhone 3G I was unable to try it over 3G. I do think a GUI interface needs to be added in for easy enabling of different apps to be tricked, but I can over look that for basically free calls where ever you have 3G, or EDGE coverage. Though not all providers may approve of this functionality and could block the necessary ports for VoIP calls, something this app cannot get around. Be aware that if your carrier doesn’t approve of this and you’re caught you could be subject to extra fees or other bad things I’m sure you don’t want.
This easily fits under the category of “Why to Jailbreak”, load up your Cydia, install this right away and enjoy some VoIP.
[Source - BigBoss] Cydia