One of our clients use Five9 call center. It does appear to work well for when it is operational. However if Java updates, it possible for the program to break. The program is very finicky, and I personally would not recommend it. Yes the program works well , however with the high failure rate... it makes it very unappealing to use as a solution. #Spiceworks
Five9 is more of an enterprise level Callcentre software - used by call centers around the world to manage inbound, outbound. It can connect to CRM of your network and you can see all the lead information on your screen including past notes, and all relevant information.
when it comes to installation, we had issues with Java for a long time and still is it an issue they haven't resolved.