A Billion-Dollar Turning Point for Mobile Apps

The path for Internet start-ups used to be quite clear: establish a presence on the Web first, then come up with a version of your service for mobile devices. Now, at a time when the mobile start-up Instagram can command $1 billion in a sale to Facebook, some start-ups are asking: Who needs the Web?

Smartphones are everywhere now, allowing apps like Foursquare and Path to be self-contained social worlds, existing almost entirely on mobile devices. It is a major change from just a few years ago, underscoring how the momentum in the tech world is shifting to mobile from computers. In that context, the Instagram deal looks like something of a turning point, as even the Web giant Facebook tries to get a better grasp on a market that requires a rethinking of old rules.