Fuze Voice was widely adopted as it is our main phone system. Most of their features are used company wide and we haven't had any issues getting new hires to use their systems. The only system that is a bit underused is the desktop app. While it is used for meetings, the chat feature isn't used much outside of my department. I think that has more to do with everyone being more comfortable using Google Hangouts as it is right there in the email account when they sign in, and not another app that needs to be opened.