You maybe have met the Advantage before - perhaps at a CompUSA firesale (CompUSA being one of the few places you could score an advantage). The Advantage is a strange duck, it's a Windows Mobile device with a 640x480 resolution touchscreen and a little separate keyboard. While it's technically a smartphone, it's certainly not something you'd want to hold up your ear (doesn't work that any anyhow). Still, though, it's an interesting concept and could be just the sort of in-between device you've been looking for.
Enough exposition: HTC is announcing that they're upping the specs on the Advantage today, it's now the X7510. What's changed? Well they've fixed up the keyboard by adding in haptic feedback, doubled the memory to 16 gigs, updated TouchFLO, tossed in Opera 9.5 (or will, that is), and pumped up the battery to 2100mAH (!). You still get the Triband HSDPA/Quad-Band EDGE + WiFi + 3.1MP camera + Bluetooth + tilt-sensing G sensor + GPS (TomTom included).
It may not be the smallest little guy around, but HTC makes up for it with some power, hey? Oh, and it's going to sport a “Future Version of Windows Mobile” when it's available in March. Cue the ORLY owl.