I was just searching the web for the answer to this exact question. I hope someone replies.
After using WinMo phones, I've decided that I simply do not need all the features of a smart phone (web browsing, particularly). However, one that I appreciated a lot was threaded messaging with SMS. I was disappointed with the messaging/"feature" phones AT&T had to offer-- the LG Xenon's "threading" is far from what you get in an environment like WinMo. So, I've been looking for a non-Windows Mobile phone that has threaded messaging (I'm on AT&T but don't have a problem unlocking a phone). A full keyboard is nice, but I've learned to tolerate on-screen ones, too.
Is it too much to ask for this? I can't be the only one who has wanted a middle ground here between "standard" phones and smart ones.