Paying for internet WiFi? That's SO 2010. If you have one internet connection on your iPhone 3G then you can share that connection with just about any other device, such as the iPad, iPhone, iPod, laptop, XBOX 360, and PS3.
This method of tethering will only work if your iPhone is jailbroken.
This works even with an iPad or iPod-touch without 3G. So press "play" and learn how to save major moolah while still getting your daily fix of "Vampire Diaries" on Hulu.