I have created open source android SMS and Messanging app available under Apache Licences V2 here on my github link :-
Shh! Keep your voice down!
This App is used to demonstrate the use of rsa cryptography to encrypt the message.
This application supports to all languages.
This app currently supports to encrypted SMS and emails.The user with private key could decrypt this messages.
Public key may be shared with anybody and user could encrypt the messages using it, but the owner of private key will able to decrypt the messages.
We will implement voice data to encryption in future.
Any volunteer help, Suggetion and modifications are welcome. I would like to request guys to crete a pull request if any one have good idea.