Hi

It sounds like you tried to connect your ATA (WAN port) directly from your modem, is this correct? and did you have the radio button "dynamically assigned by DHCP" selected? It is generally best (if you are having problems) to get it working in front of your router first, for testing purposes and then work on moving it behind.

For the device to work behind your router - you need a couple of things. The router has to be set up to forward ports 5004-65000 UDP and make sure you have an IP address available from your router that is outside your router DHCP pool.
Your ATA settings: the IP address should be the local IP address that is assigned or outside of your router DHCP pool locally above. Your subnet mask is good. Your default router should be the local IP to your router. The DNS Server 1&2 should be a DNS server, I would use one of these DNS servers:

Service provider: Google
• 8.8.8.8
• 8.8.4.4
Service provider: ScrubIt
• 67.138.54.100
• 207.225.209.66
Service provider: dnsadvantage
• 156.154.70.1
• 156.154.71.1
Service provider:OpenDNS
• 208.67.222.222
• 208.67.220.220
Service provider: vnsc-pri.sys.gtei.net
• 4.2.2.1
• 4.2.2.2
• 4.2.2.3
• 4.2.2.4
• 4.2.2.5
• 4.2.2.6

Remember to reboot everything (modem, router, and ATA) after making any changes. Not necessary if just making changes to the ATA, in that case just reboot the ATA.

Hope this helps.