I haven't been keeping track of what is going on in the MP3 player market, but I haven't seen advertisements for MP3 devices that can communicate with each other.  Why bother downloading music from the Internet when you can just get them from friends you meet or passing strangers (via Bluetooth).  Are there such MP3 devices?

Everyone of the MP3 devices has some means to upload music into it so all you need is a device that either download or resample from one MP3 player and upload into another.  Eventually, you won't even need the bridging device when MP3 songs can be beamed across devices with a single button.

Hmm.  That turns each MP3 devices into a inbox of sort.  Receiving messages from secret admirers and ads from street vendors this way could be a little surprising though.