Fabrial Telephone

[Green chicken]

If you were to conjoin two rubies, the rubies would be able transfer sound waves as long as there isn't any aluminium in the way. Using the principales of a Tin can telephone you would be able to transfer sound waves into the ruby through a wire, and transfer the sound waves out of the other ruby using a different wire. Using two such devices, you would be able to make a fully functioning telephone.     

[mathiau he/him]

If you use the distance increaser Navani discovered in RoW then yes, you should be able to do that, otherwise your waves won't be transferred due to the damping by distance

[theTruthshaper]

Hmm, this stuff just depends upon how small a you can make a ruby and still fit the spren in it. I don't think what I think you are saying would work with a large ruby.

[Zanarkand]

I'm waiting for the heating fabrial-powered steam engine. Probably won't happen though, they would instead use fabrials to power their machines directly like they already do with pumps and lifts, etc.