The answer is, "well, yeah, I guess, if you really wanted to..." but why? I suspect it reflects a desire to try something cool with their iPhone which they already have, so then, "All I'd have to get is that little projector and a screen-thingy like that!"
Which really is great. I know I sound like I'm laughing at them, and it is kind of amusing, but it is also great that people think DS is cool and want to try something with it. And at some point, this could make sense. But the great thing is that this is one of the great advantages that we, in the DS and DOOH field have, is that our stuff is (potentially) really cool.
But not guaranteed cool. Again, CONTENT (and method) is KING! It's about effective use of our cool gadgetry. It's all about effect and business-related results! We have absolutely got to keep our eye on the prize, which is to produce a business result.
Cool, exciting imagery will sell some systems, but a measure-able ROI-related result is what wins the game. Make sure you, too, don't get too caught up in all the features and benefits of your system, software and components. If you are not working with top-flight content or content producers, you need to change that, right away. If you don't know where to look for that, let us know. If you have a superior content producer that has produced great content that produces ROI for you, let us know as well; we are always interested in winners.