Even though iOS 4 supports multitasking, the multitasking capabilities are limited to a small set of specific situations—and instant messaging isn’t one of them. If you switch from an instant messaging app to another app, the IM app doesn’t keep running as usual in the background, waiting for the next message to arrive. Ordinarily it pauses, suspending its operation in such a way that when you switch back, it can instantly pick up where you were before.
This means that if you’re running an IM app, that’s normally the only thing you’re doing—you can’t have a chat going in a corner of your screen while you work on something else. (Well, you can, but only within limits—keep reading for details.) And, if that’s how you like to do things, fantastic, but for many people accustomed to having lots of applications open at once on a computer, it may feel quite limiting.
One partial solution is push notifications. If you use an IM app that supports this feature (most do) and you turn it on, then you can remain logged in even when the app isn’t running, and a pop-up alert appears whenever you have a new message. You still have to switch to your IM app to read or reply to the message, but at least you’re not completely out of the loop.
Another approach is to build other features (Web browsing, Twitter, Facebook, or whatever) into an IM app—or the other way around. Several such multitasking apps exist (as I discuss just ahead), and if you use one of them, you can do several things at once, but only within the limits of what the app offers. Still another way to have your cake and eat it too is to use a Web browser that lets you display multiple pages on the iPad’s screen at the same time (see Multi-pane Browsers, ahead), and use a Web-based IM client in one of them.
Source of Information : TidBITS-Take Control of Working with Your iPad 2011