I personally don't trust the released video (or, I should say, the audio) for the following reasons:
1) The guy doesn't seem to have an Iranian accent. The guy talks more like an Arab; he talks from the bottom of his belly. See this funny video: "Arabs vs. Persians" for dummies!
2) The so-called Iranian voice is unexpectedly very clear. Considering that he is on a speed boat at top speeds and exposed to open air, his voice should be very noisy. In this video, the American guy who is inside an enclosed cabin sounds a lot noisier than the guy on the speedboat.
3) The so-called Iranian guy talks very calm as if he is talking dirty: I ammmmm comminggggggg toooo youuuuuu..... (the American guy in a heavily-armed warship is more nervous than the so-called Iranian in a practically-defenseless speedboat!!)
4) The Bush administration has a history of fabricating evidence! (Remember Iraq's WMD evidence? Remember the American-style date-format on Iranians' Iraq-involvement evidence? Remember the stolen laptop that had information about Iran's non-existing Nuclear-Weapons-Program? And this)