OK, short story:
The IDS is no longer manufactured or supported by a manufacturer. It ceased to have new parts manufactured for it when InterTel bought Executone.
A company called Aable Communications is liscensed by Intertel to support the Executone systems. I know very little about them.
The IDS is a very good system. The only major issues that I know of are that it requires a modified Wyse 60 monitor or a PC running the correct terminal emulation to program it at all. There is no programming that can be done through a phoneset. Also, because of when it was discontinued, it does not and as far as I know will never support VOIP.

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Intertel Telephone Repair
Toshiba Telephone Repair