Howard Rheingold's latest book, Smart Mobs (details and a blog at http://www.smartmobs.com), is fairly essential reading on the future (and past/present) of mobile communication and social exchange.
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for productivity/sharing apps, try:
openCOLA (http://www.opencola.com)
swarmcast (oss version)(http://sourceforge.net/projects/swarmcast/ )
and
thebrain (http://www.thebrain.com/)