At Microsoft in the UK we have all been issued with the Orange E200 Smart Phone as our mobile phone. Now whilst I am not very keen on phones I have been impressed by what these smart phones can do (see http://blogs.msdn.com/michael_platt/archive/2004/06/17/157937.aspx).
These phones are beginning to be the hub of new mobile communities or social networks as moblogs which are picture based blogs. There are a number of new ways of creating communities based around the phone as discussed in http://socialdesigner.net/GDC2004/index_files/frame.htm which has interesting and wide ranging implications. One of the first of these is community based games such as http://www.mogimogi.com/ , a mobile phone based sort of treasure hunt.
I can see a number of other community based applications and aspects using the location, picture and communication capabilities of these smart devices. I think this will be an interesting area to monitor going forward.