If you have the time and inclination, and a certain sense of daring, you can share your cellular data as a Wi-Fi signal for free, without connecting through your data carrier. I’m not a huge fan of jailbreaking, per se; even the non-jailbreaking solution seems a bit technical, and some folks might see it as borderline unethical.
If you fall into either camp, and want to set up your qualifying iOS device via your cellular data carrier, here’s how.
First up, you need to know that this will only work with a cellular data provider which allows the Personal Hotspot feature on your iOS device. You may lose an older unlimited data plan as well, as carriers like AT&T won’t enable your Personal Hotspot feature with an unlimited plan; you’ll need to switch to a newer plan.
Secondly, you’ll need an iPhone 3GS or later, iPad (3rd generation) Wi-Fi + Cellular or later, and iPad mini Wi-Fi + Cellular in order to make this happen.
If you have all that in place, simply launch your Settings app with a tap, then tap the General button. Next, tap into the Cellular area. Tap on Personal Hotspot, and then toggle the switch on the next screen to ON. You may get a dialog box telling you to contact your data provider; you can do so either on the web or by calling them.
Once Personal Hotspot is on, you can enable a password and then connect other devices, like a Mac, iOS device, handheld gaming device, or any other Wi-Fi enabled device you might have. Keep in mind, though, that the more devices using the Personal Hotspot, the more data you’ll use up.
Source: Apple Support