Usually people ask me, how to make a free mobile ringtone?
I use this way: convert AAC to MID files to use MP3 files as mobile ringtones:
First - you have to take a clip of your MP3 that is no longer than 20 seconds or so
Second - you have to get a copy of Nokia Theme Studio (you can find it here), or other mobile ringtone converter
Third - Create a theme with Theme Studio and insert the ringtone into the theme on to your phone
Fourth - save the theme on your phone (in themes directory) and then activate the theme
Done! Your ringtone will work now at your mobile phone!