Resonance Stones are magical items capable of transmitting sounds great distances. They are sometimes called "rocky-talkies".
Resonance stones are a type of stone that naturally resonates with sounds in their vicinity. If two stones are magically tuned to one another, sounds near one stone will be projected from the other, and vice-versa. Usidore gave a stone to Otok Barleyfoot for his quest1, and received regular updates from the road.2
Tuned resonance stones are rare enough that they would not be an efficient way to broadcast a podcast.3
The Space Bunker is able to listen in on untuned resonance stones where ever they may be naturally located in Foon.4
Resonance stones can also be used to store sound, and Spintax the Green has used them for the audio version of his book, the Pandenomicon.5
Sigint the surveillance spider has revealed that the Dark Lord is able to eavesdrop on Resonance Stone conversations around Foon. Resonance stones should be placed in a cold cellar to ensure absolute security.6