Preview at WWDC likely in June, followed by September launch.
Flashlight App Sneaks Tethering Into App Store (For Now) [Pulled]
Nullriver was the first to offer an unofficial tethering app, NetShare, for the iPhone in late 2008 though it was quickly pulled from the App Store and never became available again. Based on that reaction from Apple, it's likely that Handy Light will not remain in the App Store long either. Apple also has previously informed developers that such "easter eggs" must be declared in apps when submitted, so we don't expect Apple will take kindly to this hidden feature.
HandyLight sells for $.99 [iTunes link] and written instructions on how to use it have been posted at AppShopper.
Update: App has been pulled from App Store:
Handy Light reached the #2 in the top paid apps listings before being pulled.