My reasons are easy.
- Voice dialing - not yet on BBerry. I use Voice dialing + a Sony Ericsson BT headset when I'm driving or walking around--don't have to look down and either hit speedial or look up a number
- I'm already on a cell phone contract for my Nokia
- I like the feel of metal phones
- We don't have number portability in Canada (yet)
- Because I'm silly
I use the BBerry for data only. If I didn't have my cell phone first, I would've used the BBerry as a phone + data device.
Has nothing to do with the voice quality of the BBerry, at least not in my case.
Perhaps some other folks might also find the integrated cameras in their phones useful (I don't).