First off, I am totally unfamiliar with phone system operations, setup, etc. in general, but am smart enough to figure out just about anything thrown at me. What I have is a controller, model #3501-00 SFE900411. The phones show that they are Starplus STS 24 button DKTU part #3515-71, ISS:1 Rev: 1.3.

I'd like to add an on hold message that I have saved as an mp3 or wav file. Is this possible with this system and what are the steps to making this happen?
TIA