Here is a barely used phone system (PBX) with music on hold. Very snazzy, supports mp3s. Please check below site for more will receive the unit itself and the power adapter. The software for it, which can be used to make your own music on hold, can be downloaded from the company's website.

On Sep-06-08 at 13:01:04 PDT, seller added the following information:

update: I incorrectly called this a PBX. Please note that it is JUST a music on hold system. Please see my other listing for the PBX I am selling.