Although push notification has been out for weeks now, plenty of publishers are still integrating the technology into applications for the iPhone and the iPod Touch.
Yahoo is one. Earlier this week, Yahoo updated its instant messenger application to version 1.21 (previous coverage). The update's content and form are identical, with the exception that it can now push an instant message alert and notification to you when the Messenger application is closed, so long as you're logged in. In addition to seeing the semi-transparent window with the message contained within, Yahoo Messenger will list the number of missed messages you've accumulated in the red, circular badge overlaying the icon.
Message alerts are accompanied by a chime, which you can change in the settings (Settings-->Notifications-->Y! Messenger). If your ringer is silent, receiving a message will make the phone vibrate instead.
Another change is that the latest version keeps you logged in for two weeks at a time, even after closing your application. Of course, since Yahoo has not enabled simultaneous sign-ins, the second you log onto YIM from another location, you'll boot yourself off the iPhone.
While there aren't many substantive alterations to this new version of Yahoo Messenger, there are a few tweaks. Yahoo has rolled the Contacts list into search, so you can easily fire off texts to contacts who are not necessarily Yahoo buddies.
Yahoo Messenger has also welcomed "buzzing" into the fold. You know, when you want to get a friend's attention by shaking things up. Yahoo reads your firm phone-shake as a buzz, but neither you nor your recipient feels a vibration or hears a sound, so it's a small, somewhat thin implementation.
In addition, Yahoo Messenger 1.2.1 gives you options to turn off the landscape keyboard, and the app also resolves a bug that previously showed empty groups in your contact list.
You'll need to have iPhone software 3.0 installed to take advantage of these changes.