Hi Evgeny,
I defined at ser.cfg to listen on port 5066 instead of default 5060 port, saved changes and restarted the SER.
As a consequence you also should - change the DNS SRV records to point to port 5066, - or configure all clients to use the SER-IP:port as an outbound proxy.
At Wireshark sniffer I see that there is an ICMP--> Destination Port Unreachable response on all sip REGISTER requests arrived from various endpoints at my setup.
Obviously these are related to REGISTER requests addressed to the default port, where SER does not listen anymore.
As far as I understand this means that configured 5066 port is not bound with SER application.
No. 5066 is bound to SER application, but the ICMP messages are produced by SIP requests targetted to port 5060.
Franz