Raseac secure phone is a free software for Windows Mobile 2003/5.0 Pocket PC and Smartphone devices that allows you to make secure encrypted voice calls to any landline or GSM phone from your mobile device.

It supports two types of encryptions:

-256 bit AES encryption
-571 bit Elliptic Curve Cryptography encryption

And there are two versions of this software:

1) For Cellular and landline calls with 75 seconds of conversation for each call
2) Only for landline calls with unlimited time for each call.