One of the new features that Apple will launch with iOS 5, which is expected to launch shortly, is iMessage, it is basically a unified chat messaging service for the iPhone, iPad and iPod Touch.
Now according to a recent report from the guys over at Mac Rumors, Apple is also building iMessage into OS X Lion’s iChat service, which would mean that he iMessage service would also be available on Mac OS X Lion devices as well as iOS devices.
This would mean that you would be able to receive and send messages through iMessage no matter what device you are using, whether you are using your MacBook or iPad you would still be able to use iMessage.
Obviously this is another feature that Apple wants to unify across all devices, in a similar way that they did with FaceTime, which would give the service many more users than if it was only available on iOS devices.
Source Mac Rumors