Many entities, both individuals and companies, record their phone calls. In many jurisdictions this is made legal by there being a recorded message at the start of the call informing the other party about the recording, and giving them an opportunity to hang up if they do not agree. Jurisdictions where this applies include the UK and California I think.
It must happen quite frequently that these recorded messages are just played to another recorded message saying much the same thing, and then when humans actually get to talk neither party is aware that the other is recording the call. This could also happen for other reasons where humans are not immediately connected.
What is the legality of the recording in this situation? Is the presence of the message enough to count as consent, even if it is not heard by a human? Is the message irrelevant if no one hears it so this is as if it was not there (and therefore the recording or its use is illegal)? Is the fact that one party is recording a call enough for the other to do so, even without either party being aware of the others recording?