I've never, in all my years, had an FA ask me to stop listing to music on an iPod or iPhone. I've also never had them stop me from taking pics during takeoff/landing. And a few weeks back on ATL-SLC, a girl in front of me was watching a movie on her mother's iPad, and kept watching till touchdown. FWIW I've been in F, J, and Y (but mostly Y), and my iPhone has always been more than conspicuous. I've even seen one or two e-readers being read. However, I have seen FAs request that things like laptops be stowed, and I always assumed it's because they're larger and heavier than a music player or tablet.