IPtel
From Guardian Project Wiki
IPtel is a free SIP service sponsored by the SIP Express Router developers. It supports ZRTP but does not support secure SIP.
Network scan results
lee@ikaruga:~$ dig SRV _sips._tcp.iptel.org ; <<>> DiG 9.7.3 <<>> SRV _sips._tcp.iptel.org ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 2386 ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0 ;; QUESTION SECTION: ;_sips._tcp.iptel.org. IN SRV ;; AUTHORITY SECTION: iptel.org. 86384 IN SOA ns1.iptel.org. hostmaster.iptel.org. 1325497017 360 1800 604800 86400 lee@ikaruga:~$ nmap iptel.org Starting Nmap 5.21 ( http://nmap.org ) at 2012-03-09 15:04 PST Nmap scan report for iptel.org (217.9.36.145) Host is up (0.20s latency). rDNS record for 217.9.36.145: sip.iptel.org Not shown: 992 filtered ports PORT STATE SERVICE 22/tcp open ssh 80/tcp open http 443/tcp open https 5060/tcp open sip 5061/tcp closed sip-tls 5080/tcp closed unknown 5087/tcp closed unknown 9090/tcp open zeus-admin