RFC 2806: a URL scheme for describing phone numbers. A URL looks like
tel:+1-312-555-4589. Cute. I didn’t know this existed. But Mobile Safari on the iPhone does. It seems more immediately useful than hCards (browsers already understand it!) But much more limited in scope: its scope is expended on standards for modem and fax calls. Wow. Retro.
I’ll be keeping it in mind, I believe it will become more important.