Can We send data using exisiting power outlets in homes
X-10 is a system developed nearly 40 years ago (1975) which is designed to send control information over the power line to turn devices on and off, etc.  It consists of controllers (transmitters) and receivers.  Being so old, you can find hundreds if not thousands of devices on eBay that you could hack.  Of course you can also buy new ones too from many suppliers.

There is even a library for Arduino that allows it to send and receive X-10 commands.

And here is an application note showing how to do X-10 with a PIC16.