I also agree that RTMT helps although I think a network management tool provides better end-to-end access to view QoS, jitter, latency, etc. Unfortunately we don't have one but I've seen demonstrations from IR.com and SolarWinds and MS has a network management system that provides some tools.
If you need to help remote users with desk phones, I recommend Uplinx which is a phone emulation tool that lets us see what the user is doing on the phone. It also lets us remote "touch" the device so we can troubleshoot problems reported by the user. This really helps when we are trying to work with remote users.