I have not done any tethering but when I asked the Cingular Data support they asked if I had the $44.99 BB plan or the 69.99. I said the 44.99 and their reply was, that plan does not allow tethering, you need the 69.99 plan.

Now I do not know if I wanted to tether on the $44.99 plan if I actually could, even if I was ok paying data usage fees. Cingular said it was not capable-which I have learned to not 100% beleive until I actually try it myself.