How many of you must carry both with you everywhere?
What is the optimal screen size of tablet for you all? 7"? 10"?
Do you wish to have a phone with a bigger screen size?
Since I don't make a lot of calls, I have a cheap, non-smart, pre-paid cellphone, primarily for emergencies, and so that my wife can get in touch with me when I'm out. I have an inexpensive 7" Android tablet that I use primarily as an ebook. I have a netbook that I use when travelling, and a PC with a pair of big displays as my primary work machine at home.
In my opinion, a 10" tablet is too large to conveniently carry everywhere, and a phone's display is too small for reading on (for me at least.)
Optimal screen size of tablet? N/A - I have no use for one. Between a smartphone, a netbook, and a largish laptop, I don't need another gadget. (Recently, I've seen those "keyboard stands" for the iPad, and guess what: the contraption looks just like a netbook, while costing 5 times more; what's not to like?)
My wife has a Samsung Galaxy Note (5.2") as her primary phone, a G-Slate (7") and an Asus Transformer (10") with keyboard dock. The Galaxy note is the winner for her, as it is the only one she carries nowadays. It used to be both an HTC Amaze (4.2") and a 7" tablet.