Reading the upcoming iOS 5 support for build-in notification of earthquake in Japan, makes me wonder if there is a standard for distributed realtime notification protocol. One that is similar to DNS, Whois, IRC, NNTP that is replicated across servers. From a user point of view, one can subscribe the channel for the notification source, and get alerts push down to their mobile device or desktop. For example subscribe to Tsunami notification from the official source of your country. Or traffic congestion alerts from the traffic police. Ideally the protocol needs to be location aware, that means send alert on New York traffic news when you are in the city for example. Not sure it is a kind of application for AMQP. With such a standard in place, then delivery can be a plug-ins for iOS/Android notification, SMS/MMS, Gowl on your Mac or Twitter. Or maybe I'm taking about a Twitter application?
The nice thing about standards is that you have so many to choose from (quote by AST). That said, XMPP Publish-Subscribe pretty much fits your description: <a href="http://xmpp.org/extensions/xep-0060.html" rel="nofollow">http://xmpp.org/extensions/xep-0060.html</a>