A good messaging service between iPhone and ipad?

I have brought my lad a iPad and I have a iPhone, so just want to see if there's a good messaging app that we can speak to one another, We're both using the same Apple ID, cheers

Use the built in 'Messages' app, I believe with the newest iOS (software update) all of the iDevices have it now, it's pretty much the exact same thing as text messages except it's free and you can use your iPad, iPod, iPhone, all of them to chat with each other. If you want more of a face-face chat you can use the FaceTime App. Skype is also another good one. But if you just want a nice and easy built in app use the Messages one, just add his Apple ID as the number and text away!

You can read more on it here on the Apple site! Https://www.apple.com/ios/messages/