The possibility for alternate reality games will be immense, but I suspect that's just scratching the surface. We've only had this smartphone technology for what? 5 years or so? And so far all ours uses for this technology have been fairly superficial and mundane (by which I mean, if you'd gone back a decade and asked people "what would you make if you had a smartphone that could do x?" you'd probably get decent predictions of the present day). But in 10, 20 years I imagine it'll have evolved to something far beyond what we can currently imagine.