From Gandalf Studio:
Wp Ringtone Maker helps you make your own Ringtone with your .mp3 files. When you come into a song and you want to make into your own ringtone begins at the exact position, this app can make that happen easily. Due to the limitation of Windows Phone 7.* OS, you can't make a mp3 file your ringtone unless it's within 39 seconds and not larger than 1MB and genre of "Ringtone". However, this app can help you manipulate this limitation and enjoy making your own Ringtone file for your device.