Direct from Twitter:
TweetDeck AIR, TweetDeck for Android and TweetDeck for iPhone will be removed from their respective app stores and will stop functioning on May 7. Our Facebook integration will also stop on May 7.

Why is Twitter shutting down Tweetdeck service?
Over the past 18 months, we’ve been focused on building a fast and feature-richweb application for modern browsers, and a Chrome app, which offers some unique features like notifications. We’ve recently introduced many enhancements to these apps –– a new look and feel, tools like search term autocomplete and search filtersto help you find what you’re looking for more quickly, and automatically-updating Tweet streams so you immediately see the most recent Tweets. Our weekly web releases have been possible because we’ve nearly doubled the size of the TweetDeck team over the past six months (and we’re still hiring).
What Tweetdeck services will be available?
According to MacRumors, Twitter will continue development on its TweetDeck web app and Google Chrome apps, with a secondary focus on its native Mac and PC apps.
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