Ambriel,

As long as your NAT is set up properly, and your firewall is forwarding the proper ports you should be fine. Keep in mind that not all VoIP carriers are the same. What works on some may not work on others. For example some VoIP carriers prefer if your NAT is turned off as they handle it from their end to your equipment, while others will work whether the NAT is on or off. Ports; some carriers require many ports to be opened for udp while others require only one, or different ones. Always check with your carrier and compare and contact their support to find out if there is anything they can do.

- Tom Bradshaw
Link2VoIP.com