Even thow 3CX is a very easy to use PBX, their focus relies way more on marketing and buying market share then on improving the actual product. There is much room for improvement in several areas. For example their Phone App - getting calls from another line is simply not possible. Also there is no support for mp3 files, and the quality of the wave files that can be used have to be really, really bad quality in order to be accepted by the system. also the licencing model is a rip off in my opinion. who wants to rent sofware in order to keep it updated? the perpetual licence quickly gets really expensive if you need a more then 8 lines and there is no company that needs less.
Pros: Easy to install, use and manage
Cons: Expensive, Way Limited Functionality for a "world class" product