From: http://www.pcworld.com/news/article/0,aid,116005,00.asp

Future OS will track all your contacts regardless of the type of communication

Chief among Longhorn's capabilities is a communications history from which you can manage everything, says Paul Erickson, development manager for Windows communications. From this central location, you'll be able to sort and filter messages by various themes such as name of sender or date of conversation, he says.