After collapsing, exhausted, inside he recorded an audio message to say he could go no farther.

A coughing sound heard on the audio message left by the perpetrator increased suspicions that the bomber had other accomplices.

Its signal would appear scrambled, with an audio message being played that described the service and provided a phone number to subscribe.

All actions, such as dialing, playing audio message, recording, are initiated by human, normally by the press of a key.

And there could be sports services that update fans on their team's progress via audio messages.