About a year ago, Apple released iOS 5.0 for iPhone, iPad and iPod touch. One of the biggest new features of iOS 5 is the ability to send messages over a data-only connection. In real-world terms, this means an iPad, even a wi-fi-only model, could send and receive text messages with other iOS devices. This feature is called iMessage, and it really is a nifty feature, but it can be hard to understand the difference between normal text messages and iMessages on an iPhone. Enter Jesse Hollington, Applications Editor at ilounge.com, a great resource for iPhone/iPad/iPod information.
In a post on Quora (which is awesome, by the way), Jesse very clearly explains the difference between traditional SMS/MMS (green text messages) and iMessage (blue messages).