It would be nice if they had more data in their network, e.g. a dump of the Facebook graph that they could match to the phone records they used, so that they had information on parent/child relationships and romantic connections. I wonder if social networking companies would be open to cooperating in such research.

Of course, it opens a can of worms on the privacy front. I'm not sure where they got the data from that they used, but I can't help but wonder how they could legally do this research, since prima facie any use of phone records for this purpose would be against most EU privacy legislation. (not saying they did anything 'illegal', just that at first glance it seems to be at least pushing the envelope).