does this comdial support a single line cordless phone and what opx adapter is needed for interface

It needs an ATI-D, an analog terminal adapter. That adapter supports 2 analog circuits and ties into 2 digital ports.

Comdial also made a proprietary cordless phone called a Scout, a 900mhz digital phone. I never had the opportunity to work with one, though, so I can't say if it worked good or not. I would imagine that they would be somewhat hard to get, though--but maybe not.