Maybe it's a simple thing I've overlooked, but here's the situation:

IBM RS/6000 Server running on AIX 4.3.3 in a LAN enviroment with IP
PC users are accessing the server with PuTTY using the TELNET protocol
(port 23)
I've tried to access it from out of building offices using port
forwarding on a SpeedTouch 780 modem, but when I open PuTTY with the
ip address of the modem and port 23, it access me to the Speedtouch
instead of the server.

Followed the instructions on on configuring the modem.

What could be wrong?