Apple has begun sending out invitations to select media outlets inviting them to a special event on March 17. As illustrated in the invitation, the topic will be iPhone OS 3.0 and a new software development kit (SDK) for the updated operating system; the event will be held on Apple’s campus in Cupertino, CA. The invitation arrives a little over a year after Apple’s 2008 iPhone Software Roadmap event, in which the company outlined plans…