Just days after the successful launch of the iPad, Apple sent out invitations for a media event at their Cupertino headquarters scheduled for April 8th, at 10:00 AM Pacific Time. The invite banner, which can be seen above, leaves no doubt that the company will be previewing the next major version of their mobile operating system, iPhone OS 4.0.

Apple is widely expected to unveil new multitasking capabilities along with a user interface refresh. One feature nearly certain to appear in the new iPhone OS was promised to a concerned customer by Steve Jobs himself in an email sent from his iPad: a unified email inbox for the iPhone Mail application, similar to an identical feature found in the desktop Mac OS X Mail application.

Due to the timing of the event, the location, and the expected refresh of Apple’s laptop lineup, they may choose to unveil new Macbook, Macbook Pro, and Macbook Air models sporting IPS display panels and Intel “Arrandale” processors during or some time after the event.

Do you have a “must have” feature you would like to see Apple include in iPhone OS 4.0? Leave a comment below, send us an email, or drop us a note on Twitter!