This will be an invitation only event at Apple Town Hall and will give those invited a preview of what to expect from iPhone OS 4.0. Previously Apple have done this for iPhone OS 2.0 and iPhone OS 3.0
Don’t expect a release around that time. But do expect clarification on things like OS unification (i.e a single OS for iPhone, iPod and iPad), and multi-tasking.
We’ll keep you posted.
Let us know in the comments what you are expecting, or hoping for in the 4th major revision of Apple’s mobile Operating System.