Hi, I just have installed Asterisk and configured SIP.conf but My Zoiper phone can’t register. I activated sip debug and no output is received. I run The TraceBuster to analize traffic and show that the sip registration request is been sent to Asterisk but asterisk don’t Respond. Both have 5060 udp port configured.
From another pc you can try to connect to the sip port with telnet or try a port scan with nmap (the first should be simpler).
Which Linux distro are you using ?
I don’t use CentOS so I can’t help you much, here is a discussion about the firewall of CentOS 4: gidforums.com/t-13827.html , perhaps it could help you, or try read the documentation about CentOs or ask it the related forums about the firewall.