I suggest against using phones. XMPP or IRC are nice, use your own private hidden service if you want, OTR + Tor...you can even do all of these things from your phone if you really need the portability a phone offers. Then you will have encrypted and untraceable text communications, although if you use a phone your movements can still be tracked (then again they can probably be tracked pretty well if you use a laptop too, unless you make sure to very frequently spoof your MAC address).