
old stowger.
You are far from the first to ask these questions.
One, the current system is analog, ie., two pair. Even though the Merlin 820 uses the 8 position plug, it is still only two pair.
Two, look for a digital system. They are one pair.
Three, almost all systems today have MOH and Paging either onboard or with an option card.
Four, Cheap is as Cheap does....oh, I think I heard something like that before. A new or refurbished system can be a better investment. That way you know you have a warranty, manuals, and tech support (depending on the purchase).
Five, Don't buy name....I assume you will be installing and maintaining it....get a system that is user friendly. Some major names are somewhat involved and not as end-user friendly.
Six, Look for one you can get parts for....a ten year old system may have problems getting repair parts ten years from now.
That being said, look at the top of this page. You will see tabs indicating manuals, systems, et.al. And of course, the Tech Talk board.
As kenb said....Avaya Partner. Lots of equipment out there, easy to get parts, easy to administer, and user friendly.
Good luck, old stowger. Let us know how it comes out.