I emailed my wife a request to head over to our local staples to buy a HD on sale. I attached a jpg of a coupon I thought she would print out and use in the store, but she was out of the house so she walked into the store and showed the clerk my email on the iPhone instead. Nice guy, he found what I wanted from the email description, and they were off to the check-out counter. Here is the cool part: the clerk scanned the barcode from the iPhone screen, and the discount was given without fuss! He mentioned that most phone screens are not able to be barcode scanned with their devices. His experience was iPhone only. This is a 3GS iPhone, so I presume the 4G should be ok too.