In the basic version you can make 10 simultaneous calls with a 20 user system. In the pro version you can make 20 simultaneous calls with a 20 user system.
You can add a maximum of 20 users to a basic pbx 20 user system. It will not allow the 21st user to be added. It will only allow 10 simultaneous calls or voice mail checking. I hope that answers your question.
Thanks and you have answered my question.
Next question is regarding "click to call", can any one help to advise how to disable the "response "succeeded: ID number",
after the "click to call" has been activated?