SHAFAQNA – The Grand Ayatollah Sistani answered a question about recording telephone conversations and playing them for others.
Question: There are devices which record telephone conversations without the knowledge of the speakers, so that they can be used for summoning or producing a witness when needed. Is this allowed?
The Grand Ayatollah Sistani: It is not Wajib to ask permission for recording conversation of the person talking on the phone, but playing it for others is not allowed if it is considered as insult or revealing the secret of the believer; unless it is in contention with another equal or more important Wajib.
Source: PERSIAN SHAFAQNA