New company WhatSim, daughter of ZeroMobile allows people to send Whatsapp text messages internationally for 10 euros a year.
For sending pictures, voice messages and videos needs to be paid with a prepaid credit system:
Every 1000 credits will cost 5 euros.
http://www.droid-life.com/2015/01/21/the-whatsim-will-give-you-whatsapp-access-anywhere-in-the-world-for-free/#more-160003
http://www.whatsim.com/en