The iPhone already has the popular Twitter app but now comes an upgrade release of the Tweetie and it's the Tweetie 2. Tweetie 2 is now available at the AppStore for $2.99 and is a separate app then that from the original Tweetie, therefore, you will be required to hand out another $2.99 if you want the upgrade. Some of the new features of Tweetie 2 are listed below:
*Seamlessly handle multiple Twitter accounts
* Explore all of Twitter, from your own timeline and mentions, to the favorite tweets of your followers and friends
* Full persistence: more than just caching tweets, Tweetie 2 restores your entire UI if you quit or get a phone call
* Fantastic new offline mode. Read, tweet, favorite, follow, save to Instapaper and more even when you don't have a connection. Your actions will be synced as soon as you go back online
* Full landscape support (configurable of course)
* Live-filter your tweet stream
* Post photos and videos, even configure your own custom image host
* Vastly improved compose screen with recent hashtags, @people picker, URL shortening and more
* Compose screen multiple-attachments manager
* Drafts manager ensures you never lose a tweet (and you can even send drafts to Birdhouse)
* Link Twitter contacts to Address Book contacts
* Follow, unfollow, block and unblock from multiple accounts simultaneously
* Saved searches sync with Twitter.com and the upcoming Tweetie 2 for Mac
* Autocomplete recent searches and Go-to-user
* Threaded Direct Messages and improved conversation navigation
* TextExpander integration
* Rich integration with Follow Cost, Tweet Blocker, Favstar.fm and more
*Edit your own Twitter profile
* Specify custom
API roots on a per-account basis
* Nearby map view
* Translate tweets
* Preview short URLs
* Safari bookmarklet support for easily sharing links
* In-app rich text email composition
* Tons of little things, including improved avatar caching, auto-refresh, refresh-all, seamless Twitlonger support, hashtag definitions and more
via:
MacRumors iPhone Blog: Tweetie 2 Arrives in the App Store 
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