Raseac Secure Phone 3.0
the author of this app says:
This phone application uses a modem as a data channel to send encrypted voice over telephony line. The fixed telephony system is freeware, with unlimited number of calls. Our system works with cellular telephony, and uses the GSM-CSD (Circuit Switched Data) circuit. The voice is encrypted with Advanced Encryption Standard (AES) cryptography with 256-bit encryption keys. We use the CBC mode with Random IV, and the user can choose his keys. You only need a 56k data modem and a PocketPC to have a secure phone. Using a Windows mobile PocketPC 2003, users can have cellular communications, and with a SDIO modem users can have fixed line connectivity. Our system works with cellular-to-cellular, cellular-to-fixed and fixed-to-fixed telephony.