Is it possible to catch voice audio stream with java (JME or Android), custom encrypt it and then send it as regular stream via regular GSM call? And off course decrypt cipher on other phone. Is application level java permitted to intercept audio stream or it is disabled on hardware level?
Are there already apps that do that?
Mobile networks perform lossy transcoding on voice channels, for example with
Therefore I doubt that an encrypted voice data stream survives transmission via a mobile network in a way that allows decryption on the receiving side.
Simple analogy: audio -> encrypt -> MP3 compression -> MP3 decoding -> decrypt -> audio. This may not work. Or: if you make this work then you have a chance of transporting the encrypted stream via a voice bearer.
Your option would be to do that on a data bearer, transporting the encrypted voice via IP. But this requires a separate telephony application on the mobile devices.