I recently got a new cell phone with unlimited data from AT&T. I do not, however, have tethering included (using phone as a modem for PC/laptop). Does anyone know how much I'd be charged for tethering? I already used about 1800 MB of data.

I think you will be charged an extra $15 per month (someone correct me if I am wrong) if you want to add tethering.

Depending on the phone, you might be able to tether for free if you jailbreak (iPhone) or Root (Android) using 3rd Party Software.

i agree, most android phones can be rooted and you can download free wireless tethering or even wired tethering apps from the market

wireless tethering has existed for a long time now and they're just now starting to think of how to capitalize on it.

also, AT&T might be different but i know T-Mobile's unlimited data plan is only 10gb a month of total bandwidth