HDMI support is available in Motorola Droid Bionic which is not found in iPhone 4 and most probably will not be there in iPhone 5. How do you hook it up to your HD monitor? The short answer is that you don’t. The maximum audience for an iPhone screening is one or two. You want more? Use your laptop and hook that up, or your desktop machine. Apple offers expensive HDMI adapter to please a few geeks.
Of course, I’m always wanting to hook my phone up to my HD monitor. Ridiculous.