It all depends on your fone , my nokia plays mp3, acc, mid and mxmf files. If you have an older fone then memory will fill quickly, one of my mp3 files is 2mb.
good luck
oh yes, you can get phone managers for various makes of fone, nokia and sony erricson i think motorola do, you need to be able to plug in phone to puter via usb, other cabled link or Bluetooth (so named after a viking guy).
These suites will do the conversions for you.
good luck again
I have a nokia system I am sure i can upload it somewhere
zet