It's official: more than half of Americans now own smartphones. The truth is, most of us probably would have guessed this figure to be much higher. The percentage is certainly growing, however, presenting a number of opportunities for retailers to engage with consumers on an individual basis and when they're most likely to purchase. But consider the flip side: slightly less than half of America, or about 155 million people, is still without smartphones. Instead of leaving them in the dust by focusing exclusively on mobile-only campaigns, retailers should seize the opportunity to close the gap by engaging both audiences where it matters most — at the point of sale.