DO NOT DO THIS IF YOU HAVE PORTED SIRI TO YOU DEVICE, IT WILL PUT IT INTO INFINITE LOOP!!!
Follow me on twitter and check out my tutorial how to port siri to you device (manually or through cydia)
http://www.youtube.com/watch?v=kPpgWjlWJvE - full siri port
http://www.youtube.com/watch?v=JW_2SOVzq2E - simple full siri port
I guess you could do all that. OR you could go to cydia and download MY3G which will allows you to choose which apps you want to fool into thinking your 3G connection is Wifi. Very simple and it works.
It is a native solution, not a mod. the Apple boys have left this out of the file code, but putting it back in allows for iOS to execute other code. It's like this: Cheat codes for video games are NOT hacks, they are purposely placed and coded in to the game. The only reason the phone needs to be JB is because there's no other way to get to the file. You could navigate to the file through SSH rather than buying (*or stealing) iFile as an alternative.