- SSH into your iphone to /Library/MobileSubstrate/DynamicLibraries/VoIPover3G.plist
- Copy VoIPover3G.plist to your computer ( and btw , back it up )
- Open the .plist file ( if you are on a mac use Property List Editor )
- Add the bundle identifier of the desired app into the .plist file
- Copy the edited .plist file back to your device.
- Reboot device ( not respring )