These will allow all normal functions including external extensions.List of default ports used by the 3cx phonesystem:
5060 (stanard sip port) TCP/UDP
5061 (secondary sip port) TCP/UDP
5480 (portgre) (only on local machine)
5481 (apache) (only on local machine)
5482 (media server) (only on local machine)
3478 (STUN Server) TCP/UDP
7000-7500 (Default port for internall calls) (only on local machine)
9000 - 9003 (ports for external calls through VOIP Gateway) UDP
10000-20000 (RTP ports) (Used if no stun available for audio)
On the local machine, if firewall equipped, I would just open those for all options. Shouldn't be a security risk if confined to the LAN only.5060 (stanard sip port) TCP/UDP
5061 (secondary sip port) TCP/UDP
5480 (portgre) (only on local machine)
5481 (apache) (only on local machine)
5482 (media server) (only on local machine)
3478 (STUN Server) TCP/UDP
7000-7500 (Default port for internall calls) (only on local machine)
9000 - 9003 (ports for external calls through VOIP Gateway) UDP
10000-20000 (RTP ports) (Used if no stun available for audio)
Founded in 2005, when VoIP was an emerging technology, 3CX has gone on to establish itself as a global leader in business communications.