WikiPock has compressed the entire Wikipedia under 4GBs (not including images). The software cost $9.99 and allows you to search and read Wikipedia articles in your Windows Mobile, BlackBerry, iPhone/iPod touch, and Android smart phones without internet connection. The application gives you offline access to the full content of Wikipedia in several languages. Data is stored in your phone's memory and not downloaded from the network. Access is fast and do not require any data connection.
It’s currently supported languages include: English, German, French, Polish, Dutch, Italian, Portuguese and Spanish. It requires a 4GB or 8GB microSD memory card to use WikiPock, and particularly if you are interested in multiple languages.
More info: WikiPock