Have a customer with 2 of these phones that is determined that she can have Music On Hold without paying the Centrex company to pipe the music down. Sent her a Music On Hold player with regular phone jacks inputs to test and she notified my that her phones use a prong jack. Any advice as to what phone cable end is used and if there is an adapter made to go from her cable to a standard phone jack....or advice in general on adding music on hold to these phones.