Ipod or MP3 for hold music; mono adapter?

We are in need of a new music server for our on hold music here at the office. We have been using a 5 cd changer on constant shuffle & it has never really worked to our satisfaction. I am Ipod Mp3 illiterate so please bear with me.
First can this be done? It needs to run 24/7 and I don't really care about quantity of songs.
Second it need to be able to be plugged in and charged of course & able to stay on play in case of even short power putages.
Third (and this may be a hangup) it needs to be in mono. If there isn't a player that will play in mono, can we plug in a mono headphone jack or use a stereo jack and run the L&R legs together?
Any insight would be awsome.
Thanks for your time, John