My cell phone can play music and podcasts, but I have a separate device for that. Indeed, most of the podcast-addicted gadget geeks I know have separate portable audio devices and use their cell phones primarily as phones.
Why? I can speak only for me.
The primary reason is battery life. It takes a lot of juice to power that fancy Windows CE color screen.
The phone has over three days of stand-by (demonstrated), but only about five hours of talk time (that’s from the specs, but it’s consistent with my experience).
The music player has demonstrated about 15 hours of playing time (also consistent with the specs).
(I do have an ebook reader on my cell phone. Great for doctors’ waiting rooms.)