We are using 3 sites. One site hosts the 3CX server, and one IP Phone. The second site hosts an ATA, and one IP Phone. The third site hosts 2 IP phones. After some resets, we were able to get the two phones at site 3 to register with the server, but when we call the voicemail system, we get no audio. We are also unable to dial between extentions. After a period of time one of the phones will nolonger be registered with the server. At the site with the 3CX server, is a Verizon FiOS router. Ports 5060 and 9000-9049 are open and pointed to the 3CX server. At site 3 (the ones with 2 phones) we have a Linksys wrt54g2 firewall. The phones are Linksys SPA941 running firmware 5.1.8 as documented. I think this is a firewall issue, but putting the server in a DMZ does not seem to help the issue. Any help would be greatly appreciated. Hopefully I have articulated the issue well enough.