Core issue
The PIX/ASA firewall does not allow Telnet connections to its outside interface.
Resolution
Telnet is an insecure communications protocol, so the PIX/ASA does not allow Telnet to its outside interface. You can Telnet to any other interface of the PIX; if you run PIX Software versions 5.2 or later and have a VPN-DES activation key, you can use Secure Shell (SSH) in order to connect to the outside interface of the PIX.
Refer to the SSH - Inside or Outside section of How To Perform Authentication and Enabling on the Cisco Secure PIX Firewall (5.2 Through 6.2) for more information on how to use SSH with PIX.
Refer to PIX/ASA 7.x: SSH/Telnet on the Inside and Outside Interface Configuration Example for more information on PIX/ASA version 7.x.
