Whispersystems has released two Android apps that allow for encryption of all calls and texts with any other device running the apps.
RedPhone allows for encrypted calls using SRTP and ZRTP between you and other phones running RedPhone. Setup is simple and use of the app is seamless. All calls are VOIP, and the encryption documentation can be found here:
The other app, TextSecure, allows for both asymmetric encryption between you and those who also run the app as well as local encryption of text messages. You can even set a timeout so that your messages are locked after X minutes/ hours – a very handy feature.
In light of recent disclosures about US wiretapping, PRISM and otherwise, you may want to seriously consider trying these out.
You can download both of these apps off of the play store: