I've been slowly becoming convinced that communication is the killer app for ubicomp. There's actually more to this statement than is immediately obvious, because researchers have been talking about ubicomp for nearly 15 years, and have come up with lots of applications, very few of which are compelling. Seriously, does anyone really want their refrigerator to tell them to buy more milk?
Communication seems to be the key in many past applications, ranging from email to instant messenger to cell phones. By mixing location technologies, wireless communications, and multiple modes of input and output, ubicomp might be able to make new strides in this area, lowering barriers to entry and increasing the richness of communication with others.
Apparently, this is something that some social scientists have been arguing for a while (so my colleagues say), but only recently have tech researchers started thinking along these lines. Besides the basic human need for communication, the act of communicating seems to create a network positive effect. In other words, if I send a message, there's a likely expectation to receive a message.