Regardless, I see nothing but problems with a barcode system on phones. The general public can't even handle the fingerprint checker at the front gate. Now allow them to do it through their iPhone? HA!
Sorry, but most people who have the iPhone get it becuase "they can", not becuase their tech marvels. How would you like to be in line behind the yuppie mom of 4 demon children while she tries to figure out how to get the barcodes to display on her iPhone? Do you REALLY think she has that on the screen BEFORE she gets up to the line? Remember now, she would have to go through the bag check first. So she would have to get the phone ready AFTER the bag check and BEFORE she got to the turnstile.
Good idea, but like most technology, as soon as you add in the average human intelligence, you got some real problems. As George Carlin brilliantly pointed out: "Think of how stupid the average person is, and realize half of them are stupider than that."