The lads at Telco 2.0 are busily dissecting whether Facebook is a threat to the carriers. Doesn't seem likely to me, and neither does it seem that way to them. But once you get past the initial assessment, the analysis is a vintage piece of telepocalyptic work.
Perhaps the most interesting observation is contained in the diagram of the Telephony Interaction Pyramid, which shows that the area of overlap between social networks, and telephony is around "conversations", which they explain in a distinctly web-oriented fashion as "A conversation may involve a sequence of interactions with some common purpose, initiated in different directions, and potentially with a varying set of participants. An email or newsgroup thread is closer to the meaning here. Telephony includes some limited “conversational” features, like missed call alerts."
The implication is that there is great potential for partnerships between telephony companies and social networking companies, and presumably (given the distinctly anemic uptake of initiatives like the SkypeMe application on Facebook) that partnership revolves around the management of those conversations on voice networks as opposed to IM and email networks.
Heady stuff, and worth a read.