In the context of a telephone call via an operator-assisted service, is it fact that in AmEng, if the operator asks the service user (caller) if they are through, what is meant by that is, are you done/finished with your call?
Thing is, considering that AmEng and BrEng share the idiomatic put someone/something through [to someone], which has the exact same meaning on both sides of the pond (i.e. to connect someone/transfer someone's call [to someone]), I can't seem to figure out why from the perspective of AmEng, the phrase are you through, Sir/Ma'am when used in such context, would mean anything different than are you connected, Sir/Ma'am?
This is what it's all about:
Are you through? (telephone)
(UK) = are you connected
(U.S) = are you finished/completed with your call
Another Americanism which is by now quite well known in Britain, though it can still mislead if you are on the telephone and the American operator asks, Are you through? If you say 'Yes' (because you are connected) you are likely to be cut off.
FYI, these are not the only resources I've found that support a BrEng/AmEng difference in meaning of the phrase are you through in the context of telecommunications.
Fact or baloney?