I had a bad intercom in the bathroom and at the outside entry. If anyone is interested, Newell's parts staff found me the contact information for the company that makes the systems. ADI, located in Chicago, can be reached at 1-800-482-9708. They can give you the name and contact information for a distributer/reseller in your area to sell you the units. The distributor suggested I contact Fairfax Electronics in Los Angeles. They have a website
http://www.at-fairfax.com/Intercom.htm but it doesn't list the units used on my Newell. I gave them a call (323) 731-2561 and they shipped them to me.
My 1992 uses the AIPhone TD6H inside intercom units and an IE-JA door unit. The door unit was $45 and the inside intercom unit was $90. They are very easy to replace. Since we don't have windows in the door the intercom is really helpful. It is great that the company still makes and sells exactly the same units that were used 15 years ago.