The cosmic rays consist of all sorts of particles ranging from massive protons to neutrinos with little to no mass. There are trillions of trillions of neutrinos passing through the earth at any given time. While the proton, neutrons and other particles get trapped by the many layers of the crust, these neutrinos can stream through the matter unaffected. Neutrinos are extremely light and feebly interact with the matter.
The only detector which is capable of detecting neutrinos today is the Super Kamiokande Neutrino Observatory. The detector is nearly a kilometer below the surface (so that particles which interact with matter get enough chance to do so). The test chamber is made up of steel and is in the shape of a cylinder. An array of super sensitive light detectors (photomultipliers) surround the sides of the test chamber. At the bottom of the test chamber, there are nearly 50,000 tons of water.
The theory behind the detector is that some of the neutrinos that pass through the water interact with matter and produce charged stray particles in the process which travel faster than the speed of light in water (speed of light in water is approximately around $0.75c$). This shows a phenomenon known as Cherenkov radiation which is similar to the sonic boom in sounds. This light is captured by the detectors and amplified to an extent which is measurable.
Detecting neutrinos is very difficult and requires big detectors. It isn't practical as of now to use neutrinos as a fast medium of communication. Of course, most of the neutrinos pass through the earth without interacting but it isn't practically feasible method of communication.