One of the biggest gaps in iPhone functionality is the lack of instant messaging. True, you can use web-based IM like
Meebo or
MunduIM, but there is no native application for the iPhone. And according to reports, third-party apps that will be available beginning in June with the 2.0 firmware update will not be "allowed" to run in the background -- certainly an essential feature of an IM system.
Even the iPhone version of AOL's AIM instant messenger that Apple demoed back in February supposedly won't run in the background -- again, not due to any technical limitations but by design by Apple. Thanks a lot, Steve Jobs.

Now we know why Apple has put those restrictions on developers. They have their own plans for an instant messenger. We learned that Apple has filed a patent for mobile instant messaging. According to diagrams in the patent filing, it looks very much like the existing SMS messaging on the iPhone.
AppleInsider reports that Apple suggest the service could also be used for sending and receiving images and video, although the patent filing doesn't include diagrams of what that might look like.
Here's the
full patent filing.