You can send unlimited free text messages from any iOS device to any iOS device over Wifi or 3G. Technically, you can also send pictures, movies, etc. without being charged but keep in mind that if you are using 3G some data fees may apply (this pretty much depends on your data contract).
I am an Apple Certified Support Professional with over a decade of experience supporting families, schools, and businesses. Tech has always captured my imagination, but it's not my only passion. I'm an ordained Anglican minister; Aeropress is a daily ritual of mine; I've driven across Mongolia; and I'm the father of three girls. I hope to provide for you a balanced and realistic perspective into the practicality of technology.