Following the release of the OS 3.0 firmware and SDK updates less than a month ago, app devs are now stocking the App Store with new or updated apps that use Apple’s Push Notification Service.

Push notifications are used by applications to alert you of new information, even when the application isn’t running. Notifications differ depending upon the application, but may include text or sound alerts, and a numbered badge on the application’s icon on the Home screen.

You can turn notifications off if you don’t want to be notified or want to conserve battery life.

Push notification has been long awaited by iPhone and iPod touch users. Until the release of OS 3.0, Apple was unwilling to enable users to run applications in the background (or conversely, when the app has not been launched) because it said PNS would drain the devices’ batteries prematurely.

Now, apps can be always connected to an Apple server, enabling, for example, users to receive IMs without having the app opened on their iPhone or iPod touches..

Here’s a quick roundup of some of the new or updated apps capable of alerting you when you’ve received a text, IM, update or other message from developers.

BeejiveIM, from Beejive, is among the first of these apps to be available. BeejiveIM supports AIM/iChat/MobileMe, MSN/Windows Live, Yahoo!, MySpace, GoogleTalk, ICQ and Jabber, allowing users to access all of their IM clients from one user-friendly interface.

Pinger has released Textfree, which enables you to send an unlimited number of text messages to any U.S. mobile phone instead of via Simple Message Service, or SMS, for short. Sending texts over cellular networks is free, unlike sending texts via SMS, which typically run $0.05 apiece.

ngmoco updated its new Star Defense to enable players to expand their campaigns and compete with friends via Direct Challenges. In addition to Twitter, Facebook and email, players can send Direct Challenges via PNS to their friends over the Plus+ network, a free service for the iPhone gaming community.

Fans of Tapulous’s Tap Tap Revenge can now send challenges to friends via PNS.

NotifyMe (with Push) from PoweryBase has been getting good reviews since it debuted less than a month ago. It’s a to-do app capable of push reminders to pick up the milk, take care of business or anything else you might need to do by deadline.

You get PNS, but only if you want it. To turn all notifications on or off, go to Settings and tap Notifications. To turn notifications on or off for an app, tap Notifications and then select an app from the list and choose the types of notification you want to turn on or off.

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category: Breaking News, Round-Up