Windows Phone gives you the ability to add MP3 songs as custom ringtones. This walkthrough will show you how to use a music track as ringtone for Windows Phone 7 and Windows Phone 8.
These tips should also work for the Nokia Lumia 535, 520, 540, and Windows 10 phones.
Set a Song as a Ringtone on Windows Phone 7
If you want to use a music track as a ringtone on Windows Phone 7 (WP 7), make sure that the track is in WMA or MP3 format, has a maximum duration of 39 seconds, is less than 1 MB, and doesn't come with DRM protection.
To use a music track stored on your computer, you must use the Zune software.
To do this, connect your phone to your computer via USB. Doing this will open Zune automatically. Once the program is open, select the music that you want to use as ringtone and sync it with your phone. When the sync is complete, disconnect your phone from the computer.
Head to Applications > Settings > Ringtones + Sounds, and select the newly added ringtone.
You also have the option to create a ringtone with Zune. Choose the songs that you want to convert into a ringtone, right-click on it, and click Edit > Ringtone > OK.