Previewed at WWDC, launching in the fall.
Apple is Building iMessage into OS X Lion's iChat
iMessage is a unified messaging service for iPhone, iPad, and iPod Touch that allows users to send text and multimedia messages over Wi-Fi and 3G with read and delivery receipts and real-time typing indication. But as far as Apple has officially said, there is no way to send iMessages to or from non-iOS devices such as your Mac.
One developer has revealed to MacRumors that there is evidence that Apple has already started building in iMessage support into OS X Lion's iChat instant messaging software.
Buried in the framework of OS X Lion's iChat, are two new properties (highlighted below):
@interface IMMessage : NSObjectThe "timeDelivered" and "timeRead' fields indicate the tracking of delivery and read receipts for instant messages. These features, however, are not supported in any of iChat's native messaging protocols, while the same features are offered in Apple's iMessage protocol. These properties were also not present in previous versions of iChat prior to OS X Lion. We believe the only reason Apple would have added these properties was to build in cross compatibility with their new iMessage protocol.
Adding iMessage support into OS X Lion's iChat would allow iOS 5 users and Mac users to easily send text messages to each other in real time. This would not be the first time Apple has added such cross compatibility between its Mac and iOS product lines. Apple similarly extended iOS's FaceTime video conferencing feature to the Mac with the launch of FaceTime for Mac in February.
iMessage for iOS has not yet launched and will be part of iOS 5 which will be released this fall. It's not clear if and when Apple will launch iChat support for iMessage, but it seems work has already started.