You can easily open up a Wikipedia page in Wikipanion by creating a bookmarklet:

If you are on iOS 4.0 or higher:

1. Tap the export button and choose "Add Bookmark".
2. Hit 'Save"
3. Copy the following link to the clipboard by single tapping the text, moving the blue start and end markers to select the entire line, and choosing "copy": javascript:document.location=document.location.toString().replace(/http.?:/,%27wplink:%27)
4. Click the Bookmarks button to view your bookmarks.
5. Click the Edit button.
6. Select the bookmark that you created earlier.
7. Edit the URL -- that's the web address. Single tap, choose 'select all', and then choose paste to replace the current text.
8. You're done! Next time you're on a Wikipedia page, just choose this Bookmark and the page will be automatically opened in Wikipanion.

If you are on an older version of iOS:

1. Tap the plus button to add a bookmark.
2. Hit 'Save"
3. Click the Bookmarks button to view your bookmarks.
4. Click the Edit button.
5. Select the bookmark that you created earlier.
6. Edit the URL -- that's the web address.
7. Put the cursor right before the word "javascript" and delete everything that appears before it. You should be deleting the ?, the _, and everything in front of it so that the line starts with the word "javascript"
8. You're done! Next time you're on a Wikipedia page, just choose this Bookmark and the page will be automatically opened in Wikipanion.