Apple iMessage (Apple instant message) is an instant messenger service developed by Apple Inc. that allows end users to send texts, documents, photos, videos, locations, contact information and group messages over Wi-Fi, 3G or LTE networks to other iOS or OS X users.
Sending iMessages provides an alternative to standard SMS/MMS messaging and is free for users texting over Wi-Fi using an iOS device or Mac with proper software. iMessage informs users when a message has been delivered, when it was read and whether the recipient is in the midst of typing a response. Through the Apple Messages app, users can send text, photos and videos via SMS/MMS to non-Apple mobile phones over cellular networks. To differentiate between iMessage conversations and SMS/MMS conversations, Apple colors iMessage conversations blue and SMS/MMS conversations green. Messages works with a phone number and any email addresses associated with an individual's Apple ID, allowing for integration across devices. This allows owners with more than one Apple device to continue the same iMessage conversations across all devices.
iMessage was unveiled by Scott Forstall at Apple's Worldwide Developers Conference 2011 keynote June 6, 2011. The service is run by Apple's Message application and is available on mobile devices including the iPhone, iPad, iPod touch running iOS 5 or later and laptops running OS X Mountain Lion or later.