Who wants to go jogging with their cell phone, who wants to relax in the yard, soak up some sun, listen to music in peace just to worry about the darn phone ringing.
iPods have gotten thinner, and the new Shuffles (which I did break down to buy) are truely remarkable (for less than what a cell phone with intergrated mp3 will surely be)
Last lets not forget that battery life in a cell phone is a bad joke to say the least, I just don't see it happening.
If the market was going to migrate to the cell, companies like Sony wouldn't be spending Millions to compete with Apple.
Just my 2cents