AT&T flips the switch on tethering with the release of OS 4. That's clearly not AT&T's fault, it's Apple's -- the iPhone inexplicably supports only USB and Bluetooth for sharing its internet connection, even though jailbroken apps like MyWi prove that a WiFi connection is totally doable and countless other handsets already support WiFi routing. And iPad doesn't support using another device as a Bluetooth modem, either. And as long as you're paying the tethering fee, there's no reason why AT&T wouldn't want you tethering the iPad; you'll certainly be able to do it with any phone in AT&T's lineup that can create a WiFi hotspot, after all, and we're sure they'd be happy to take your overage cash once you hit 2GB regardless of the device you're using to gobble the data.
In the meantime, you know what you can tether to an iPad? A phone running Froyo, for one -- Google was certainly happy to show off that capability back at IO. Or pretty much any device running S60 from the last several years. Or a Palm Pre Plus... yeah, you get the idea.