Keith Hampton describes research findings (in press) which suggest that social interaction in urban public spaces (parks, plazas, and markets) is likely to be more diverse than interactions through wireless internet use, which in turn are likely to be more diverse than interactions through mobile use.
I think this is just what we would predict, because the serendipity potential of the mobile is negligible compared with face-to-face, and wifi use is more open to interruption than is mobile. But that doesn't mean it isn't reassuring in a way, and you can be sure the methodology was robust.
It builds on Keith's previous paper which looked at wifi use in cafes and included consideration of the possibility of
‘contextual’ or ‘neighborhood effects’ within cafes, whereby the lack of sociability of some cafe users has the potential to reduce the overall sociability of a public space.