caught on voicemail

A situation where a conversation not meant to be heard by a third party is recorded on voicemail or answering machine, due to one participant dialling a number (perhaps unintentionally) and forgetting to hang up after the call was not answered. The voicemail then activates and records the conversation. The person, on whose voicemail the conversation was recorded, can then listen to the conversation he/she was not meant to hear, and if necessary, provide it as evidence.
Such voice messages are often of poor sound quality, due to cell phone being placed in a pocket or purse, but often can be clear enough for the listener to extract the main idea.