This article explains how to use your iPhone or cellular iPad as a wireless modem for a computer when it's not within range of a Wi-Fi signal. To use Personal Hotspot, you'll need an iPhone 3GS or later or a 3rd generation Wi-Fi + Cellular iPad or later and a compatible cellular service provider.
Use Personal Hotspot on your iPhone | Apple Support
When you use tethering to set up a personal hotspot, your computer can get online anywhere your iPhone or iPad can access a cellular signal.
Once you've set up service with your mobile carrier according to that carrier's instructions, it's time to enable Personal Hotspot service on your iPhone or Wi-Fi-enabled iPad.
Tap Settings on the Home screen.
