Meh, smart phones like web browsers are inherently insecure. I did some work towards a secure communications gadget for use with an Android phone, but gave up

Meh, smart phones like web browsers are inherently insecure. I did some work towards a secure communications gadget for use with an Android phone, but gave up when I realized that there was no way to stop malware from activating the phone mic and listening in on you anyway. Also, these apps don't do much helpful to conceal metadata, which is more important than content in a lot of ways. Depending on what you are trying to defend against, you may have to go full Spy vs Spy, e.g. with spread spectrum radio or optical comms below the noise floor. My favorite saying about security is by the cryptographer Silvio Micali, who said "a good disguise does not reveal the person's height". Be careful out there.