UPDATE: It’s been pulled.
File managing app QuasiDisk received an update over the weekend that allows for tethering of the iPhone over a proxy connection. QuasiDisk likely slipped past the App Store approval policies, so don’t expect it to be available for much longer. The app is compatible with all iPhone models dating back to the 3GS, the third- and fourth-generation iPod touch, and the iPad. Apple often acts very swiftly to remove these policy-breaking apps, so grab your own copy for two dollars before it’s too late.