While familiar with the limits of the "speed of light", etc., it seems one could use the Casimir effect to send messages across arbitrarily large distances with carefully-tuned Casimir plates.

A message could be time-encoded on a carrier of a specific wavelength and then projected into the "Casimir void" between plates tuned to the same frequency. Any other equivalently-tuned plates, regardless of location, should receive a signal from the vacuum.