The smartphone features could save millions tons of paper! For instance in a supermarket, after making some purchases of everyday goods, each client leaves with a bit of paper, normally useful for a couple of days or less. Giving users the possibility of scanning a QR code or a similar one with the smartphone could avoid a great quantity of these little pieces of paper.
It's not easy to calculate how many receipts are being wasted right now, but for sure is in the order of hundred million. The paper comes from natural sources, and even being recycled it causes waste of energy and human efforts in the process.
The habit adds an extra cost for the environment and related companies and without these extra costs, the products in general could be less expensive. Then, with the smartphone reality in multiple hands now, nothing should stop companies to develop a method for being responsible with the environment and at the same time reducing costs.
There's a high chance of numerous users that prefer a digital copy than a physical receipt of purchase, and a great quantity of machines also have a screen for displaying it to the user. So... let's ask for it!