CNET received an email from prominent iPhone application developer stating that Apple has started giving iPhone OS 4.0 SDK to few developers for updating their applications. In the email the developer wrote, “Just wanted to give you a heads up that we’ve submitted an updated app for the new iPhone OS 4.0 software.”

Earlier this month we reported that Apple is preparing iPhone OS 4.0 Beta and accompanying SDK for developers that will include simulator specifically designed for the tablet. It is rumored that the upcoming tablet will use iPhone OS kernel but will have different UI, which may require updated iPhone OS to support.

It is believed that Apple will introduce the tablet later this month and start shipping it in March. We should find out more about iPhone OS 4.0 when Apple launches the tablet.