UPDATE: I have had this unit for almost 2 years now. It is connected to a UPS battery backup. I has literally been running non-stop since I set it up over a year and a half ago.
Almost all phone systems* manufactured today have Message on Hold capability, but to determine exactly what you have before your purchase a Message on Hold system, it is best to check with your phone system vendor. Need equipment?

Choosing great on-hold music keeps customers on the phone longer, and that means better service. It’s science! The ups and downs of technology. Call center technology experts Greenlight break it down pretty bluntly. Telephone on-hold music is difficult to get right because of a combination of basically two things. First, the sound quality of
This brings up the ever-present question of appropriate branding for your business. At a funeral home, Green says, you don't want an upbeat pop song, for obvious reasons. Mark Malekpour, who works at Beatsuite, a music library which sells a variety of songs specifically for hold systems, says that companies too often want popular music. "For an insurance company, you don't want something from Queen or U2," he said. "When you're choosing music for an insurance company, it shouldn't feel happy or feel good or lighthearted, because insurance is something you have to have, and you want to think, 'These guys get what insurance is all about.' " (Beatsuite's bestselling hold song is called "Inspiring Innovation," which is tagged as: "Success, achievement, and trustworthy.")