I've had a pocketpc and currently have a smartphone. I own audiovox smt5600 that works with cingular. It depends on what you want to do with it. I wanted to have my outlook calendar and contacts available on my phone and with the smartphone it works great. Here's a link that may help explain some of the differences.
http://www.microsoft.com/windowsmobile/about/faq.mspx#2
I just started using my smartphone for all my music. I got a 1gb mini-SD card (cost $70) and put in my phone and I transferred most of my mp3/wma files to my phone... In my car I have a headphone adapter going to fm transmitter (designed for iPods cost about $20) that transmits signal to an FM station on my car radio. I can now play all my music through media player on my smartphone and what is really cool is when I get a phone call it fades out the music and fades in my phone ringing.
I also have Microsoft Streets and Trips installed on my smartphone so whenever I need a map I just download it to my phone and I can use it. Here a pocketpc would really be better b/c you get a bigger screen and some pocketpcs now have GPS built in and streets and trips will work like a portable GPS
http://www.microsoft.com/streets/ProductDetails.aspx?pid=001 and tell you exactly where you are and how fast you are going....not to mention it is cheaper than buying a GPS device for your car.
Also they have pocketpc phones which are the best of both worlds.
http://www.microsoft.com/windowsmobile/pocketpc/phone/default.mspx
