The OpenTelecoms.org ZRTP stack provides ZRTP support on Java (J2SE, Android and Blackberry) and also C++. It is based on the popular ZORG ZRTP stack produced by PrivateWave.
The stack is used in the Lumicall dialer for Android
Participate in the ZRTP development community
Developers using or extending the stack are invited to join the zrtp-dev mailing list
Download / Getting the source code
Please see the OpenTelecoms.org ZRTP page on Github