iPhone got powerful WiFi facilities, when you want more of the facilities you have, you can think of using your iPhone WiFi modern and connect other devices, should say you should exploit these Apple forbidden features, if you like going off road.
Lets first understand what tethering is, simply sharing the Internet connection with Internet capable devices, mobiles, laptops PDA’s or anything that got connectivity and Internet slots. Sharing can happen across WiFi, Bluetooth or physical cables. Tethering makes use of, here in this case your iPhone to offer Internet connectivity for other devices. if you got an unlimited data usage connection for your iPhone, things are simple, you can connect your other devices by making use of your iPhone WiFi modem. Imagine if no hot-spots are available, you got no Internet card, MiFi or Wireless USB, if you got a Tethering enabled iPhone and got a data plan for it, and if its unlimited, you can enjoy connecting all devices.
iPhone WiFi modem after tethering will let you share whatever Internet resources it got heart fully with other devices. For some reason Apple got a problem in you using services of that sort, maybe they don’t like you using their product (which you bought for your money) the way comfortable with you. Once you bought the device, its yours and there is no logic Apple trying to stick their head up, and no one appreciates Apple doing it. So get your iPhone jail-breaked, install tethering applications from Cydia Application store and enjoy. these days At&T and Verizon customers get not much benefit from this, they got soft wares to block tethered Internet access on iPhone.