I know you can do it via WIFI (but probably not what you want)
other than that, you can probably sneak under the radar teathering as long as you're not transfering alot of data. Or wait until they offer the teathering plan.
i tethered using pda net because where i live i can only get hughes net or dial up...and when it rains hughes net goes out and i needed to use the internet so i tethered edge to my laptop and i have also just used it for wifi tethering too...but then a strage string of events occured and im yet to figure this out.
the att network went down in my area(no texting,no calling, no nothing) after that was fixed for some reason i couldnt browse the internet i would keep getting a server not responding msg and i called an att store and they just to restart my phone, that didnt work so i restored and for a while that seemed to have worked but it started acting up again today, i dont know whats going on.