The new iPhone is going to be called iPhone HD or iPhone 4G. OS 4 is the new operating system, which will already be installed. Just to clarify.
The details about the new phone will be released this week at the WWDC-- possibly even today, as Steve Jobs has a presentation on the docket in a few hours. So no idea what it will cost yet... but later today you should be able to go online to AT&T or wherever and find out.