BT is working on a phone directory that calculates "small world" networks. (That link, alas, is to a PR piece -- lots of words, but the tech content, she is not so much.) The system, being tested internally at BT, is designed so that when you want to look up the number of a Paul Kim or Matt Jones, it presents you the possible numbers sorted by social proximity, not geographic location. "You are likely to want the Matt Jones connected to you through Ben, Alice and Tom, not the Matt Jones who is your boss's secretary's dentist's cousin." There is one interesting bit of speculation in the piece -- while the original design was to improve disambiguation in large search spaces by adding social gradients, the project could also represent an alternate way of discovering unlisted numbers for mobile addresses: Its a switch from a list approach to phone directories -- you're on or off -- to a social map -- only show my number to friends of friends. (And within 6 months of launch, there would be people working to get the world's biggest mobile phone list, and then selling access to it...)