I'd go further than that
I wouldn't even use a smartphone as a mobile phone. Compared to my little nokia classic, they're big, slow, flakey, expensive, delicate and have a battery life so short it verges on ludicrous. Compared to my Streak 5, they've got irritatingly tiny screens and fiddly little OSKs, too.
Bigger tablets don't do it for me either. Like most netbooks, 10" tablets are just big enough to be an inconvenience. 7" is tolerable, I guess, but I rather like having something that I can stuff in a pocket and anything larger than the Streak won't even squeeze into all pockets.
Oh well. The trend towards making oversized smartphones with 4"+ screens seems like it might fill the niche in the future. Here's hoping.