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Globe-trotting iPhone users rejoice -- the official Google Translate for iPhone app is now available in the App Store.
The iPhone app [iTunes link] appears to be much like the existing Android app (launched January 2010) in functionality -- allowing users to speak to translate in 15 languages and to translate words and phrases into more than 50 languages. You can also listen to your translations spoken aloud in 23 different languages. One can also zoom in on text to read it more easily, as well -- this is a feature that the Android app lacks.
This official app basically echoes the web app in functionality, allowing one to view dictionary results for single words, and check out starred translations and history (even when not online).