I tried mp4 and WMV neither of them worked. So after trial and error I use AVI to convert my DVD's to play on the phone. Or am I doing something wrong? BTW I used DVDFAB to convert. The WMV movies were digital copies of new movies.
I use Moboplayer and found that it plays just about anything. Even more amazing, it will stream video from my PC. I use ES file explorer to pick a file on my desktop computer and then open it with Moboplayer.
Make sure they are not copy protected. Mine plays wmv just fine. Have the digital copy of X-Men First Class on it right now and plays perfectly. Was showing it off at Radio Shack just yesterday.