I have a 7" that i use as both, and i really like it. I'm going to get a phone too now, but won't stop using my tab as cell anyway.
My tab has both wifi and 3g (simcard) Since we live in an area prone to storms and severe snowing at wintertime which causes powerouts now and then, i still will be able to surf via the 3g net, which is invaluable in situations like mine. I Really recommend people to buy a pad with simcard ability, especially if you live more countryside like we do. Inbeatable to have your internet accessibility with you everywhere you go, instead of depending on wifi all the time.
The minus you have to consider is that it's a bit clumsy when you're on the move, for example restaurants, movies and so on. It's impossible to put in your pocket, trust me. That is the reason why i'm getting a phone.
If these reasons don't bother you, go ahead!
Ps. Bluetooth works fine, you shouldn't have any problem with that. Ds.
Just my 5 cents....