iMessage is an instant messenger application developed by Apple for iOS

IOS

iOS is an operating system for iPad, iPhone, iPod Touch, and Apple TV.IOS may also refer to:-Companies and organisations:* Illinois Ornithological Society, American state-based bird club...

 5. iMessage was released on October 12, 2011 to the general public.

History

iMessage was announced by Scott Forstall

Scott Forstall

Scott Forstall is the senior vice president of iOS Software at Apple Inc.Graduating from Stanford University in 1991 with a degree in symbolic systems, he received his Master's Degree for computer science, also from Stanford, the next year....

 at his keynote speech on June 6, 2011 at the WWDC 2011. The software was released as part of the iOS 5 update on October 12, 2011.

Features

iMessage allows users to send texts, photos, videos, contact information, and group messages over Wi-Fi

Wi-Fi

Wi-Fi or Wifi, is a mechanism for wirelessly connecting electronic devices. A device enabled with Wi-Fi, such as a personal computer, video game console, smartphone, or digital audio player, can connect to the Internet via a wireless network access point. An access point has a range of about 20...

 or 3G

3G

3G or 3rd generation mobile telecommunications is a generation of standards for mobile phones and mobile telecommunication services fulfilling the International Mobile Telecommunications-2000 specifications by the International Telecommunication Union...

 to other iOS

IOS

iOS is an operating system for iPad, iPhone, iPod Touch, and Apple TV.IOS may also refer to:-Companies and organisations:* Illinois Ornithological Society, American state-based bird club...

 5 users, thus providing an alternative to standard SMS messaging for all users with devices running iOS 5.

iMessage is accessible through the Messages app on either an iPhone

IPhone

The iPhone is a line of Internet and multimedia-enabled smartphones marketed by Apple Inc. The first iPhone was unveiled by Steve Jobs, then CEO of Apple, on January 9, 2007, and released on June 29, 2007...

, iPad

IPad

The iPad is a line of tablet computers designed, developed and marketed by Apple Inc., primarily as a platform for audio-visual media including books, periodicals, movies, music, games, and web content. The iPad was introduced on January 27, 2010 by Apple's then-CEO Steve Jobs. Its size and...

, or an iPod touch

IPod touch

The iPod Touch is a portable media player, personal digital assistant, handheld game console, and Wi-Fi mobile device designed and marketed by Apple Inc. The iPod Touch adds the multi-touch graphical user interface to the iPod line...

. Owners of these devices can register one or more email addresses with Apple, and, additionally, iPhone owners will have registered their phone numbers with Apple.

A user can see if the other user is typing a message. It is also possible to start a conversation on one iOS device and continue it on another. iMessage-specific functions operate only between iOS 5 devices, such as an iPhone or iPad, but, on the iPhone, iMessage can use SMS

SMS

SMS is a form of text messaging communication on phones and mobile phones. The terms SMS or sms may also refer to:- Computer hardware :...

 to communicate with non-iOS devices, or with other iPhones when iMessage is unavailable. On iPhones, green buttons and text balloons indicate SMS-based communication; on all iOS devices, blue buttons and text balloons indicate iMessage communication.

All iMessages are encrypted and can be tracked using delivery receipts. If the recipient enables Read Receipts, the sender will be notified when the recipient reads the message.

iMessage also allows users to set up chats with more than two people - a "group chat".

Technology

iMessage is based on XMPP, the eXtensible Messaging and Presence Protocol specification related to PubSub or Publish and Subscribe, the same system that's used for push notifications

Apple Push Notification Service

The Apple Push Notification Service is a service created by Apple Inc. that was launched together with iOS 3.0 on June 17, 2009. It uses push technology through a constantly-open IP connection to forward notifications from the servers of third party applications to the Apple devices; such...

. By building a unified XMPP notification system into iOS, Apple provides push notifications, push messaging, and FaceTime call notifications without having to keep multiple open connections to several different IM chat provider services, while also avoiding additional dependence upon a mobile account required by SMS.