Take a look at phones that run "Pocket PC". They are one step up from smartphones, a bit bigger but not much - only because the screen is bigger. Sort of a small PDA, nothing like as clunky though.
I upgraded from a smartphone and wouldn't go back. The useful thing is it has my full diary on it as well as my contact list / address book. That means I don't need a separate PDA for my diary / appointments. In fact if I wasn't so useless with tech stuff I could have a whole lot more on it - documents, photos, e-books etc etc.
Mine is an SPV M600. It runs on the "Orange" network here in the UK, but I don't see why the same unit (or something similar) shouldn't be available in the USA too. It is quad-band so works anywhere in the world, does all my e-mail when I'm away from my office - it can be set up for push e-mail like a Blackberry. It syncs automatically with my PC when I hook it up by USB2 lead (I think it can do that remotely too, over the net). It has Bluetooth etc. Probably a whole lot of other features I haven't even found yet and wouldn't know how to work if I did.
It's 4.2" x 2.3" x 0.8" in size, with a 2.3" x 1.8" screen (2.8" diagonal measurement - a good readable size). That is pretty neat, and it doesn't cause a huge bulge in a pocket.