You can install it here :
http://www.unyverse.com
I think it gives you the best of both world : online and offline.
Clearly the pure offline approach is not going to work : Wikipedia is growing too fast and the time and cost to download the entire articles on a removable media card is just insane.
On the other hand, the pure WEB ? WAP approach is not optimal, the reading experience is not very good on most mobile web browser, and you need to wait between each page.
Unyverse is a smart client app which :
1) The reading experience is better I think because your can scroll page by page and adapt the font size
2) You can bookmark articles and retrieve them on your unyverse web account
3) You read access offline all your previously downloaded articles, which is usefull when there is no or slow network data coverage.
4) It is faster because the entire article content is downloaded compressed, then you can read any section instantly