From bug #23558 comment #13:
The current mobile Wikipedia is really only for Wikipedia. I tried using Wiktionary today from my phone, and i couldn't run a search - i can write the word in the search box, but my phone doesn't have a way to send an Enter-like event.
This is true for my Samsung Monte, for Symbian-based Nokia phones and maybe for many others. On the iPhone the SimpleSeach drop-down works, although not without issues.
On the Mobile Wikipedia this is solved by putting near the input box a button that actually runs the search and can be pressed by the Symbian "mouse"-like pointer, by the Samsung touchscreen or by whatever there is in the other phones. Until there's a new mobile WikiMedia app, this button should be added to Wikimedia projects. Marking this as High priority - it's nearly impossible to search non-Wikipedia projects on many mobile devices until it's solved.