Adding myself to the no column
I can't see Apple shipping two versions of a device. If they are going to provide 3G in the units (which seems plausible, but not a sure bet) I can't see them wanting to support two different models (x how ever many different devices they actually announce.) If the radios are modular, and can be swapped out, well, that's another story. But they don't even like to do that with batteries, so I'd say it's just noise. On the other hand, if they have a chip that supports both frequencies (Broadcom was supposed to come through with one) or if it supports ATT 3G (and the world) + 4G which Verison will support down the road, then I could see it.
Exclusivity is what gives them the big subsidies though, and truthfully, the subsidies are all coming from the voice side of the contract. DATA is just something carriers provide because they have to, they resent that they get payed 1/10000th the price per bit for DATA compared to SMS and a fraction of the rate they get for voice. And bits are bits. So why are they going to want to offer big subsidies for the new Apple Slablet? (TM) The DATA deals for eBooks are because they are pretty useless for doing much more than downloading small bundles every once in a while. A Slablet will be consuming tons of data, and a good VOIP candidate as well.
So I guess my question is, why would Apple go so far out of their way to support two carriers when there is very little chance of significant subsidies offsetting the cost of their device? They are better off focusing all their efforts on one carrier for the most favorable data rates, and given that they have the iPhone contract coming up for renegotiation, AT&T will probably be quite compliant. AT&T may suck, but it hasn't stopped Apple from making a little bit of money selling iPhones. And as losing a voice connection is far more frustrating (for typical users, calm down!) than data spottiness, I imagine they would be ambivalent about it.
My bet is, if they support 3G, they will not give any details about what carrier will be supported until right before it ships.