Don't we already know?
The answer about text messages is no - you will not be able to send/receive text messages on the iPad.
Can you receive text message on an iPod Touch over WiFi? No. The type of 3G service the iPad receives is like mobile WiFi.
It's really not that hard people.
???
Yours is not an unreasonable conclusion to draw based on what we
do know, particularly as it relates to the experience of 3G dongle/card users on O2 and the like. However, it is far from certain that this is where we'll end up. Apple could easily - should they and ATT decide together - make available the very same Messages app that's on the iPhone (at least for 3G models).
I've done some poking around and there is no *technical* reason why a SIM (or microSIM) cannot send and receive texts simply because it's in a card, or a dongle, or an iPad, and not in a phone. It's a
business decision. Nothing more.
I have no idea how this turns out, and fwiw I'm perfectly fine confining my texts to my iPhone. But to say that we
know (and be insulting in the process by condescendingly telling us that it's 'really not that hard people') is plain wrong.