You have an Exchange Server, so I am not sure why you are testing telnet from the server to the ISP. Instead, you need to test telnet from the Internet to your server’s external IP address, which may actually and most probably is an IP address on the Cisco PIX firewall. Since you mentioned taking the Exchange Server down, did you take the entire network down? What kind of Internet connection do you have, are you assigned a DHCP address, or do you have static IP addresses? Does the server itself use DHCP or is it assigned a static IP address? If you want further assistance, feel free to provide your domain name and I or someone in the community will be happy to check external accessibility for you.