WinX Free WMV to 3GP is a video converter for Windows. It supports conversion of video files between the Windows Media Format and the popular 3GP mobile format. It can also be used to convert WMV files to MPEG-4. 3GP files are often used for video playback on cell phones and devices with small screens. This converter allows you to convert your files to 3GP, but there aren't any conversion profiles optimized for any specific devices. So you will have to do your homework and figure out the resolution of the screen of your device before you can convert an optimized file for your phone. The video resolution can be changed at the bottom of the screen. I recommend that you use the output profile "Keep Aspect Ratio" which will prevent the video from over-stretching in any direction. It might not fill your screen, but the video will look as it was intended to look.
In terms of performance, the only problem that I found using this converter was a little problem with audio. The audio track of the files I converted sounded muffled, like a low-quality MP3 song. I then realized this was because the converter increases sound by 8 decibels automatically.
The converter is very quick. If you want more features, you can always upgrade to the Platinum version, which has lots and lots of features.