Yes Nebel, you offer-up an interesting alternative . . . . . . why not some kind of ultra-low frequency communication? Just as sensical as ultra-high. Just a differrent system of detectors/receptors. Had not really thought much about that end of the vibrational spectrum - perhaps the harmonics of ultra-low base frequencies, or even beat frequencies, might be more easily detectable. H-m-m-m-m-m! Some kind of organic structures (other simply than 'ears') might be amenable.