Hi there. It would be good that you try to explain more about your problem.
You say not so very much. It could be anything, so please provide us with more details about what happens, what version you use, what ports you opened and forewarded, and what did you fill out in your other computer?
It is easier for us to answer and reply on your question.
I'm not from England or USA, but from Czech...
I'm bad in English, but I attempted
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I do on 3CX 5 and in VoIP client
I create 3CX system and some users, in my computer is all right, but in other pc NO
You need to have these ports open on your firewall - both on the 3CX PC and if going outside your network also on the router/firewall.
UDP 5060, 3478, 9000-9015
You will also need UDP ports 7000-7015 open on the 3CX PC for internal calls.