On Nokia's side, Ari Jaaksi has stated several times (with good reasoning IMHO) that they have no intention of turning the tablets into cellular phone. For what it's worth, I believe that's a good decision. I wouldn't be prepared to sacrifice rtcomm, bluetooth OBEX etc just to keep the operators happy.

I wouldn't completely rule out a model with a built-in cellular modem for data only to complement the WiMAX version and/or for markets where WiMAX is not available, but that comes with a bunch of new problems:

• people are already confused enough by the Nokia logo on the ITs, imagine the marketing and support nightmares if the specs actually stated GSM/GPRS/UMTS!
  
• most tablet owners probably already have a phone or three that they can (if the operator hasn't crippled it) use as a cellular modem for the tablet.
  
• operator data plans still have not caught up to the 21st century. Here in the UK at least it seems impossible[1] to find a semi-reasonably priced contract that does not force one to pay for a lot of "minutes" they're never going to use and does not expressly forbid VoIP/IM. If I have to remember to switch all my accounts offline before each time I bring the tablet online via a cellular network to avoid breaching the contract it's just not worth the trouble.

[1] I'd be more than happy to be corrected on this if anyone knows otherwise