<<Either the over the ear, the single sided or double sided headset.>>
This raises an interesting question (for me!) - do ATC headsets in countried outside UK function as telephones too? In the UK we have R/T in both ears but when we select telephone we get phone in one and R/T in the other. I recall that one excuse put forward many years ago for us not have ultra-lightweight headsets was that they couldn't do this. The re-wiring involved, although a 5-minute job was, apparently, impossible!