Encryption of a conversation inside a GSM audio channel?

Question

Mobile devices

Is it possible to encrypt a conversation and transmit encrypted traffic within a GSM audio channel? Those. without using the Internet, 3g, etc.

Answer 1

It is possible, at the input one signal is superimposed on the "other", at the output the "other" signal is cleared.

Answer 2

CSD - works fine in modern networks (MTS, Kyivstar), but many virtual operators do not provide such a service.
Depends not on the android, but on the hardware - a lot of new phones simply have the corresponding hardware module removed / missing.
But on the basis of a simple GSM module, you can assemble a device with the desired functionality.
If you need a quick solution, you should look for mobile programs for streaming distortion - restoring the voice / audio channel. (I think they should be)