"This call may be recorded" is such a vague and poor use of the language. The announcement can easily be understood as giving permission to both parties to record the call.

In cases where both parties need to be notified that a call is being recorded, this phrase does not help. It does not state if the call is or is not being recorded, it may be that relying on this and recording random calls may be in breach of some versions of the law.

The person in the call center will be well aware that many, if not all calls are recorded. The laws talk about a call being recorded and that one or more parties being aware that it is recorded - not who is doing the recording. If one party is aware that the call is recorded then it is just as ethical for the other party to record it also.