To use a song as a ringtone

You can set a song to be used as your phone ringtone in place of one of the ringtones that come with the phone.

Tap and hold a song in a Library list. In the Context menu that opens, tap Set as ringtone.

OR
On the Playback screen, tap the Menu Key > Set as ringtone.

NOTE

This adds the song to your ringtone list. Access the Contacts application to set it for a specific Contact entry.