Yes, from what I've gathered from the AT&T T&C, the iPhone 3G users do get unlimited data.so we do have unlimited? those who have 3g and dont' use netshare.
even with netshare they would probably see u are using alot and monitor you, but we can go over 5gb on our phone which i doubt anyone does unless they are tethering.
which phones allow tethering?
As for which plans do include tethering and which phones you can choose the plan with, the best bet for you would be to ask AT&T.