The type you might find in a conference room?
It works great... Even on a normal phone.
Its in near mint condition.
I got it from some company to test when we were buying conference phones and they didnt want it back - we went with another brand.
Its an olympia OL6010 (see picture here)
http://www.101phones.com/flypage/209...Olympia_OL6010
It goes for like $300 new.... Its just been sitting in a drawer so Ill trade it for a few plugs or like $50