iMessage is an instant messenger service from Apple.
First announced by Scott Forstall at the 2011 Apple Worldwide Developers Conference, iMessage allows users to send texts, photos, videos, documents and contact information over wi-fi to other iOS or OS X users.
When a message is sent to a mobile number, Messages will check if the number is set up for iMessage and, if it is set up, will swap the message from SMS to iMessage.
iMessage is supported by the Messages application in iOS 5 and later and OS X Mountain Lion and later.
What technology is iMessage built on?
All iMessages are encrypted and can be tracked with delivery and read receipts.
The technology behind iMessage is based on the Apple Push Notification Service (APNs), which is a proprietary, binary protocol.
Setting up a Keep-Alive connection with Apple servers, every connection made via APNs has its own unique code, which acts as an identifier for the route which should be used to send a message to a specific device.