How can I make these audio/video files work on my computer?

I have many videos with audio that I recorded with my phone. They are in 3GPP2 format, which I have never heard of before. When I move the files to the computer, and WMP opens them, the video plays perfectly. The audio is not there, however. When I upload the video to Facebook or YouTube, the audio and video both work perfectly. I've noticed I can't seem to save the videos from either of those sites. So I need to know how I can make these files work. Do I need a different program to play these? Is there a way to convert these files (for free) to a format that will work with WMP or VLC? Any suggestions on how to fix this problem will be GREATLY appreciated!