Over at The Intercept, Micah Lee has an outstanding article on secure chatting. If you need to set up secure chatting with someone or if you simply want all your chats to be free from snooping by the usual Nosy Parkers, this article will tell you how to do it.
You'll need to install Tor, a secure chat application (which one varies with your OS), and then do a bit of set up. After that, you just select someone to chat with and your conversation and the associated metadata are secure. Lee uses the metaphor of Romeo and Juliet wanting to chat so that their families can't listen in and, perhaps more important, don't know the chats are taking place.
There are step-by-step instructions for setting up a secure chat solution for Windows, Linux, and OS X. It also explains how to use the Android SecureChat application to set it up on an Android phone. The article says that SecureChat can not yet do Tor securely on iOS but from what I can tell from their site, that inadequacy has been remedied so that secure chat on mobile is also a possibility1.
Everyone with the slightest bit of paranoia should read this article. It's got a lot of good advice and even if you don't need or want it today, you may need it tomorrow. Read it and bookmark it for the time you do need it.
There's no indication in the article that a Windows Phone solution is available and, of course, I have no direct experience so Windows Phone users may (or may not) be out of luck. If you're still on BlackBerry, you have bigger problems than using Tor on your phone.