evan1, please complete your profile for us.
You didn't say what system this is on but assuming you have a TA-624 you would press intercom, 7311# for system CO call waiting and intercom 7321# for intercom call waiting.
If it is a TA 624 look under "call waiting" in your user manual, pages 3-41 & 3-42

[This message has been edited by MrGemini (edited June 18, 2005).]