It's free, and it's very easy to use. Unfortunately, purevoice files don't have the best quality sound. I recommend using wavepad first to convert your mp3 file into an 8-bit mono wav file, normalize the sound and anything you can do to clear it up (sometimes requires a bit of tweaking). THEN you drag the wav file into purevoice and save it. Here are the links for wavepad and purevoice:
Free Audio Editing Software - Download Wave and MP3 Editing Program PureVoice Downloads
edit: You may want to try something, this works on some Sprint phones and not on others. Instead of "converting" your mp3 file, try changing the file extension to something different. For example, I erase the .mp3 from the end of my ringtone, replace it with .qcp (the purevoice extension) and all of a sudden my phone plays mp3's! The people at the Sprint Store didn't believe me, and I said, "You ever head a purevoice file sound that good?"

Some phone models will play mp3 files with the false extension of .mid or .wav, you may have to go into your Windows settings to "view file extensions" so if you don't know how to do that, send me a private message.
