Just found this one this AM.
App is available on cydia.
Quote from BigBoss Site.
Developer Crash-X has created a clever app that tricks your iPhone into thinking it’s on WiFi when it’s really on 3G. This app has two really great uses:
1) You can install appstore apps larger than 10mb over the 3g
2) You can use Voice over IP apps such as Fring on 3G! (Think free phone calls, no minutes, everywhere you have 3G).
By default, his app only activates itself when you load Fring or Appstore.
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cool app