I've worked in both enviroments, one where cell phones were prohibited, and one where it was only for emergencies / short bursts.
It gets abused either way. It's the person, not the phone's that are at fault.
Everyone here listens to music though, it actually increases productivity. I can't see why you guys would ban music, unless you're employee is being an asshole about it. Whenever anyone comes to talk to me, the headphones come right off, before they even get to me.
Cell phones... We're allowed to take quick looks. it's a verbal, don't overdo it policy. Some people still abuse it... But for those that don't, we appreciate it. I have a wife and kid at home, sometimes they ask me something, and a quick 10 second reply when I'm not busy doesn't hurt.
How many times do you, or your employees stop for a minute to chat or ask someone a question during work hours? A cell phone is the same... just more "generational". It bugs me how some people abuse it though. Not simply because "They're going to ruin it for the rest of us" mentality, but I don't see how some people find it OK to sit in the corner, or hide behind a rack for 20 minutes browsing facebook.
These are usually the same people who leave 5 minutes early, and come back 10 minutes late for every lunch though.