We used to have the avaya definity product before upgrading to cisco's VoIP solution. the avaya system was nice. digital phones, solid system. PRetty easy to manage and configure, it is DOS based so it all command line configuration pretty much. Never had an issue with it in all the years we used it. they have changed the way the price out the system and charge for licenses, but if you are looking for 100 phones, it should be ok. If not going with VoIP i would definetly tell you to look into the avaya product. they have a smaller system called Merlin Magix, not sure if that would run 100 phones though, the Definity line is pretty nice though.