Yes you can. Any phone that is capable of using mp3's as a ringtone can do this (unless the music files are DRM protected).
Most current Nokia phones are capable of using unrestricted mp3's as ringtones.
How to change a ringtone on Symbian device:
Press Menu > select Settings > Profiles > select profile you want to personalize > select Personalise > press Ringtone > open Songs folder > Open one of the folders and select the song you want to use as a ringtone.
How to change a ringtone on S40 device:
Press Menu > select Settings > Profiles > select profile you want to personalize > select Personalise > press Ringing tone > Open Gallery > open Music files folder > select the song you want to use as a ringtone.
How to change a ringtone on Meego device:
Open Music player > select Songs > long press on the song you want to use as a ringtone > tap Set as ringtone.
How to change a ringtone on Lumia device:
Instructions how to create your own ringtone can be found from Windows Phone Online Entry Point at address http://gethelp.live.com. Select Windows Phone 7 or Windows Phone 8 > select the Music + Videos > select the Create Ringtones link (WP7) or Sync music, ringtones and podcasts using my computer (WP8).
Log in to your account on music.nokia.com and select your username in the top right corner and then Purchase history.
Note that a purchase history record is not available in the Windows Phone Nokia Music application, you will need to access it from music.nokia.com.
You can listen to music from different genres with Mix Radio.
The availability of this service may vary depending on your country of residence.
This may occur if the system cannot find the specified path when saving the downloaded track to your collection.
To resolve this, make sure the My Music folder is on your local hard drive of the PC being used.
To check this:
1. Open Nokia Music player.
2. Press F4 on your keyboard.
3. Select Collection.
4. To change the location of the My Music folder, select Change. This folder must be located on the hard drive of the computer and not at a remote location for example, in network server.
The settings can be changed within Nokia Music Player for PC to associate it with different audio files such as WMA, MP3 and AAC.
The music purchased from Nokia Music Store comes in MP3 format.
Refresh or update the music library in the following way:
No. You need to select music or videos you wish to share from within the Play To application.
Music purchased and downloaded with Nokia Music on your mobile is delivered in MP3 or MP4 (eAAC+) format.
Download speed may be affected by the following factors :
Browse to the album or song that you want to download and tap the price.