I'm not sure if you can use a different data plan but what I do know is that with the Android Data plan, tethering is free. And if you're rooted, search "android wireless tether" in google and the first link has an App to do so.
My understanding from June Fabrics PDA Technology Group is that rooting is not required for tethering. I used PDANet on my Treo 300, Treo 650, 700p, and 755p, and it has been a workhorse, so I would highly recommend this product. Hope this helps! Cheers, Jason
PS: I am thinking of going to T-Mobile because I need international and I am liking what I am learning about the Android...should I go for the myTouch? I really like the positive atmosphere I am seeing with the myTouch in this forum...a real contrast from what I am seeing regarding the Behold II.
My understanding is that the provisioning is different for android devices than say, a blackberry, or a winmob device [i.e. When I made the switch to the mytouch I came from a BB (and an iPhone) when I switched, the network connected me for about 20 minutes, then booted me].
Tier 3 support made the proper adjustments on their end And explained that they are different. The unlimited plan is pretty sweet though.