Any android app capable of storing "unsent tweet" then send it out when internet connection is resumed? As question, I have found something called offline twitter, but seems that it is broken in my HTC ChaCha, as I can't copy the "pin number" from twitter site back to offline twitter. Thanks.
A number of 3rd-party "social" apps have this feature.

Personally I use TweetDeck.  When Internet connection is not available, it will save my tweet, and throw a notification saying that it will be sent when connectivity is re-established.