C. Jennings; J. Reschke. <a href="http://www.ietf.org/rfc/rfc4770.txt"><cite>vCard Extensions for Instant Messaging (IM)</cite></a> January 2007. Internet RFC 4770. URL: <a href="http://www.ietf.org/rfc/rfc4770.txt">http://www.ietf.org/rfc/rfc4770.txt</a>