German GSMK offers mobile phones from HTC that run a special software that encrypts calls with 4096 bit Diffie-Hellman key exchange and with SHA256 hash function AES 256 and Twofish between Cryptophones.
Security does not come cheap. The Cryptophone G10i sells for about $2080. The clamshell phone is a quad-band GSM phone with EDGE and GPRS support.