Is it a CS1000E, CS1000M, CS1000S? And I am assuming you are trying to connect to the Call Server, not a Signaling Server. For a Signaling Server, you would need to connect a RAS session to your network, and then start a Internet Browser session with the Signaling Server. For a normal TTY connection, all of the CS1000 types have TTY connections. You may need to find out what the baud rates are set at for them, though.
The CS1000E has 2 DB9 connectors on the back that can be used as TTY ports(the first is used for the Maintenance terminal, typically, the second may need to be built in the Call Server).
The CS1000M comes in two variations, the cabinet and the chassis. The cabinet has a SDI port located at the bottom of the cabinet above the AUX port next to the grounding lug. The chassis has a SDI port located on the back labeled COM(RS 232). Both of which connect to a 3 port cable that is used for TTY 0-2.
The CS1000S has a SDI port(labeled RS 232) on the back of the Call Server which connects to a 3 port cable that is used for TTY 0-2.
All of this information is readily available in the electronic NTP suite that Nortel provides with all new system installation instead of the traditional shelf and a half of books that you used to get with a new switch. It's in PDF format, you might want to check with the installation techs who put in your PBX to see where the CD's might be.