You know how controlled the Apple ecosystem is when it comes to their devices and computers. Well, it is quite rare, but sometimes, an app or two does slip by Apple's radar when it comes to certain apps deemed “undesirable” to their ecosystem surface. The App Store review team at Apple would most probably pull off the iTether app sooner rather than later, but if you can still get this $15 app, then go ahead – where it will let you enjoy unlimited tethering from your iPhone's 3G connection to your Windows or Mac platforms.
Ubergizmo, iTether offers unlimited tethering of iPhone 3G connection