Croconaut, or Croconaut Transport Layer as we call it, takes care of transmitting all the messages within the range of your phone. You can set how often (or if ever) you wish to interrupt normal Wi-Fi connection in favor of Croconaut network. Take a look at Croconaut Messenger (https://play.google.com/store/apps/details?id=com.croconaut.messenger), this is our first app!
P.S. As you might have noticed, this is a 0.9 version, i.e. more like a beta. Feel free to comment/report any bugs you encounter! And of course, we're happy to hear your positive experiences as well ;)
P.P.S. Works on mobile phones only with hotspot functionality, for now. Next versions will work without any hotspot switching and on tablets, too.