By Prince McLean

Published: 04:00 PM EST

Apple this week enlisted the services of the Associated Press and called upon many of its iPhone developers to help stress test its new Push Notification service slated for delivery in iPhone 3.0.

In an email sent to iPhone developers, Apple wrote, "We have selected a pre-release version of the Associated Press app for iPhone OS 3.0 to create a high-volume test environment for our servers."

The test application, which requires iPhone OS 3.0 beta 5, will be active over the next week and will then expire. During that time, "AP will be sending a high-volume of real news alerts" to give Apple an opportunity to monitor how well the system works and what optimizations can be made.

Originally planned to arrive last fall, Apple's Push Notification system was delayed after the company realized that it had underestimated the demand third parties would make of the system.

After realizing its original design would not adequately serve the needs of developers or users, Apple pulled the plug and returned to the proverbial drawing board to create a supportable system that was up to the task of serving alerts to the audience of tens of millions of iPhone and iPod touch users.

XMPP pubsub and push notifications

Apple's new iPhone 3.0 push notification system for sending alerts from third party application developers to mobile users is believed to use the same technology as its push notification system for MobileMe and the push notification system planned for Mac OS X Snow Leopard Server.

In all cases, the alert being "pushed" is minimal, essentially a tweet that indicates more information is ready. The notification alerts act like an instant message because that's exactly what they are; an analysis of MobileMe push messages indicates Apple is using the open source XMPP (eXtensible Messaging and Presence Protocol), used in Jabber.

In addition to powering basic Jabber instant messaging in products like GoogleTalk and Apple's iChat and iChat Server, the XMPP specification also supports pubsub (publish and subscribe), a feature that enables XMPP clients to post XML data to a Jabber server, and then allows other client systems to subscribe to the node and receive a notification whenever the data changes.

This powerful feature enables all sorts of applications, and Apple's apparent use of it to power everything from application alerts on the iPhone to email, calendar, and contact changes in its MobileMe cloud services and its server product only hints at the future possibilities and potential of the technology.

Apple's extensive use of the open source XMPP pubsub technology also highlights the absurdity of rumors that the company was about to buy Twitter, a private and proprietary messaging system that has been described as "SMS for the Internet."