Default ports used by Zoiper 3 are:
SIP: 5060 *
IAX2: 4569 UDP
RTP: between 32000 and 65535 UDP
STUN: 3478 UDP / TCP
* Zoiper Free runs on UDP while Zoiper Biz supports TLS over TCP and then port 5061 is used
Using custom ports for outgoing connections:
This setting is per account.
Open Settings -> Preferences-> Accounts -> select your account;
Add the port value right after the VoIP server hosthame (IP adddress) in the Domain field.
sip.example.com will become sip.example.com:6060
The same approach is to be used for configuring a custom port for the Outbound proxy
Using custom port for incoming connections:
This setting is configured globally.
Open Settings -> Preferences -> Advanced -> Network (sub-tab)
There you can configure custom ports for incoming connections for SIP, IAX2, RTP and STUN.
Using random ports:
You can configure Zoiper 3 to use random ports for listening to avoid network restrictions in certain NAT environments.
During the activation process, Zoiper BIZ will try to connect the cert server on port 443 TCP