Tone Dials specifically, are able to record and replay sounds spoken into the, akin to an audio recorder.
Dials in general are strange, mysterious devices made from the remains of particular shellfish. Dials store energy and matter itself, usually by that particular type of energy or matter being absorbed by a tiny hole or holes on one side of the Dial.
As long as they are not used or damaged, Dials seem to be capable of storing their contents indefinitely.
The type of Dials are:
and some non-canon ones: Mad Dial and Control Dial