Yeah we have headsets in the planes with no mics and one way communication is all that is needed, so I can tell my passengers what they are looking at and whats up if the **** hits the fan, but they are going bad and I told my CFI I would do some research as to what to replace them with.
Sometimes when they are right behind you they tap you and ask questions about really prominent features that I am very obviously going to talk about anyway, plus talking during radio communication would become quite an issue.
In the pax compartment of the 207 there are only headphone jacks anyway, so the majority of intercom systems in larger aircraft, id imagine, are probably all one way.