As a company that repairs and sells refurbished telephones, I am hoping that I can give you some insight.
Selling out of service equipment is a lot like selling a used car. You can put in the leg work (via E-Bay) and get a little more. Or sell it to someone like me and get less.
The value of OOS equipement varies tremendously based on age and manufacturer.
For instance, the market is flooded with refurbished Norstar equipement, you will get less for that than, for instance, OOS InterTel phones, that cost an arm and a lege new so that people are always looking for refurbs. For us, especially with older systems, the primary value is the telephones themselves. That said, different refurb houses tend to focus on different manufacturers.
Good luck!
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Intertel Telephone Repair Toshiba Telephone Repair