Use Cases and Deployment Scope
We have used 3CX for over 10 years. As a PBX, we never had any issues it was working fine. In terms of customer service however this is not the case. The 3CX customer service simply doesnt exist unless you want to pay extra for things that should work. We currently renewed our license for another year, and the system still shows that the license is expired. Their "customer service" team says since the portal shows the license is updated, its our fault and we need to pay extra. Something which is not and we have the proof. Last year we had the exact same story, they charged us the 75 EUR support fee and their reply was to uninstall and reinstall.
Alternatives Considered
FreePBX, Sangoma Asterisk and formerly from Digium