I was just at a prospect that wanted to replace an Avaya Partner system and was appalled that there was a box (that was bigger than the entire pbxnsip CS410 phone appliance!) to facilitate music on hold! One great feature of a PC based phone system is that you can just plop an .mp3 or .wav file in a folder a have music on hold! 3CX and pbxnsip Windows phone systems both allow this.
When I was attending the SMBNation session on ResponsePoint I'll admit I was surprised that you needed to plug a mp3 player into the RP phone system to get music on hold other than the default music.
Take a look at this royalty free music for your PC phone system:
(and gloat a little that you don't need a big music on hold player to use it! ;-)