Is GSM telephony feasible on the Samsung Galaxy Tab 8.9?

I'm looking to buy a small tablet to use as a "table phone" for use with a headset, and for video telephony. GSM telephony is a must - I don't want to rely entirely on Skype, or Internet connectivity in general. (Plus I'm eligible for a landline number on my mobile contract so people can call me from normal phones for free, which is great.) I am hovering between the 7" P1000 Samsung Galaxy Tab and the more expensive, newer 8.9" one. The 7" one officially supports GSM telephony. Various tests remarked that it's a bit too chunky for use as a normal mobile phone but for my use case on the desk, that doesn't matter. I really just want something I can carry around in a bag, and put on my desk to make calls with. The 8.9" one supports GSM telephony, but doesn't come with it activated out of the box. You need third party Android products in order to use it. This strikes me as odd, and makes me expect problems - why else would one build in the functionality, but not ship with it enabled? Telephony is the one thing I really, really need to just *work* - I can't afford to deal with dropping connections, bad voice quality, patches, and an overall "beta" experience. Is telephony feasible on an 8.9" Samsung Galaxy Tab?