someone out there will invent a device which a detachable phone built in, we're sure of it.
It is not hard to find (on this funny thing called the internet) gadgets that turn your iPad Touch into a phone. I am sure it won't be long before there are things available for Andriod Tablets where the maker has decided not to include the ability to make phone calls or even give you proper 3g access.
So in a corporate environment then by all means buy your staff iPads, Play thingies or whatever. Add this type of widget and you are all set.
None of this frankly archaic thing called tethering please.
The RIM solution is pure 'lock-in'.
They won't be alone in this.
IMHO, the first tablet/pad maker to include the required h/w in their tablets along with the software to make calls will certainly carve out a pretty good share of the market. Just keep those headsets guys as it is going to be as embarrasing to be seen holding said pad/table up to ones ears as it was to be seen with one of those early mobile phones. Remember those bricks?