The encryption is 4096 bit Diffie-Hellmann (Key Exchange) and the voice and data is encrypted with AES 256 and Twofish. There are no backdoors, verifiable by independent researches.
The latest Cryptophone is the Samsung Galaxy S3 with the full encryption suite of secure messaging and voice over IP calls on any network; a hardened Android operating system with granular security management; permission enforcement module that controls access to network, data and sensors; baseband firewall that protects against over the air attacks; and a two layer storage encryption system.
VoIP or PSTN landline cryptophones are also available with the same encryption and security as the mobile and satellite phones. The servers provide trunking and presence services for the phones.