Using this as an umbrella page for the Messages app and the iMessage protocol/service.
Messages is an Instant Messaging software application developed by Apple Inc. for its MacOs X and I[[OS]] operating systems; it also supports SMS on the IPhone. Messages replaced IChat as the native Mac instant messaging client with the release of OS X Mountain Lion in July 2012. While it inherits the majority of iChat's features, Messages also brings support for iMessage, Apple's messaging service for iOS, as well as Face Time integration. http://en.wikipedia.org/wiki/Messages_(application)
The iPad and the iPod Touch gained support for Messages with the release of iOS 5.0 on October 15, 2011. Unlike the iPhone, which now supported SMS, MMS and iMessage, the iPad and iPod Touch only supported Apple’s iMessage protocol. With iMessage, users with iOS 5 could now send text, picture messages and contacts over WiFi or 3G to other iOS 5 devices without using their carrier quota.
The full-version of Messages for MacOs X was released on July 25, 2012 and included with Mountain Lion. Messages replaced IChat, the default IM client since Mac OS X 10.2. In addition to supporting Apple’s new iMessage protocol, Messages on OS X retained its support for AIM, Yahoo Messenger, Google Talk and Jabber.
Messages also came under fire due to multiple cases of Apple’s I Cloud service going down. Messages relies on iCloud to send and receive iMessages.
iMessage-specific functions operate only between machines running iOS 5 or later or running Mountain Lion or later, but, on the iPhone, Messages can use SMS to communicate with non-iOS devices, or with other iPhones when iMessage is unavailable.
iMessage also allows users to set up chats with more than two people - a "group chat" (Group Messaging). However, the group chatting features do not integrate very well with members in the group who have a different type of phone.
If the iPhone is running iOS 5 or greater, the messaging app will send text messages as an iMessage instead of the usual text message. This means that if you are sending text messages with an other iOS 5 user, there is no SMS charge associated with the messaging.
While there are sources that claim the iMessage protocol is based on XMPP, the protocol is actually based on Apple push notifications (APNS) - a proprietary, binary protocol.
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