I know of only one possibly viable, practical (temporary)solution that I would be confident in.

There are 2 problems to remember when securing your Android device, #1 is that because Android is not open source, it is more likely to have backdoors in it for the NSA, just as Windows or Apple products do. For that reason it will be vulnerable even with encryption tools such as Redphone so long as Anddroid is installed. This is akin to how HTML5 video tags (and scripts etc.) can leak DNS info while you are on the TOR network, usurping the security it provides.

Secondly, even if you put an open source alternative to it such as Replicant on the device, there is the fact that all network traffic is being monitored. This is where encryption comes in.

Now as was previously mentioned, encryption over these networks can cause problems with call quality. So the only alternative I can think of is this:

1. Use an open source OS such as Replicant
2. Make calls via WIFI rather than the cellular network and encrypt them.

Now no2 is a bit tricky because most people prefer Skype which will also allow such calls but it's a Microsoft product and will never be secure. So the trickiest part is to ditch Skype and convince your circle of colleagues to do the same, in favor of a SIP application such as linphone or CSipSimple and use something that encrypts it as securely as possible such as the FREE Ostel.co service.

The details on doing this, as well as lots of excellent tips and links to securing your data from the treasonous cold war being levied on us by traitors in the NSSA can be found at:

http:///prism-break.org

Now this will mean that you will need to use WIFI(not 3g etc.) to make calls, but if security is important to you, then you will adapt to this or just keep it to yourself.