Using Comcast Modem for DHCP and Have One Static IP

Hi,

I am a new comcast customer as of today.  Prior to today, I had a T1 with a static IP address.  Now, I have the comcast router and connect that to a switch.  I added a static IP address so that I can access my PBX remotely.

The comcast modem connects into a switch with the offfice pc'c connected to that.  I have connected the PBX to the comcast modem as well.

Gateway: 75.144.xx.142

Public IP:75.144.xx.141

Lan: 10.1.10.1

LAN DHCP enabled

In the firewall settings I have the first two boxes checked.

I have tried just about every configuration available but cannot seem to get access into my PBX.  From what I've read in the forum, it sounds like all I need to do is assing the public ip to the pbx. IF this is correct, does that mean the gateway, public ip,and subnet are programmed into the PBX server or am I completely confused?

Thank you very much for your assistance.