If you only use it occasionally, there's an app that should work for you:
Tether.
You can get it on Crackberry.com -- it's a little pricey, but it works through your phone's data plan so as long as you're not on it 24x7 and spending hundreds of dollars on iTunes,
you should be fine. I got mine half off during a deal of the day on crackberry..... there's other sites that offer discounts.