Chatting over WiFi or Bluetooth

if you want to create an android app i would suggest visiting the xda developer forums or android forums.

if you want to chat instead #andchat is great although it uses web based channels which you can create for free. you can use an anonymous username as well.

or.. we have a multitude of instant messaging apps out there which do the exact same thing you want except they require a username and password which really is no huge deal.