iMessage enables users to send free messages to other iPad, iPhone, iPod touch, or Mac users.
It’s a bit like texting, but unlike an SMS text, the message is sent over an internet connection and so doesn’t require a monthly plan. If you can get online, you can use iMessage completely free.
To receive messages from others they must know the phone number or email address that is registered with iMessage. To find this, open Settings, select Messages, and tap Send & Receive.
Once you and another user know each other’s details, you can exchange texts via the Messages app. Your conversations will also appear on your other registered devices, so you can switch between your devices and carry on chatting.
To tell if you are sending an iMessage, the Send button will turn blue and all the messages you send will have a blue background.