1. Open iTunes and find the song you want to use, it can be any song and it does not matter if it is an MP3 or AAC file
2. Launch GarageBand
3. At the welcome screen select Create New Music Project
4. Give it a name (e.g. ringtone)
5. Click create, you will see the default virtual keyboard and a track that is called Grand Piano marked in green
6. Close the virtual keyboard by clicking on the red X in its top left corner
7. Select Track from the menu bar and Delete Track to delete the default track
8. Switch focus to iTunes and simply drag the track from the iTunes window to the GarageBand window
9. Your tune is shown in an orange bar in the track automatically named the same as the song
10. If the track is not placed at point zero on the GarageBand ruler, simply drag it to the left until it is
11. Double-check you have the right song by clicking GarageBand’s play button
12. Take this opportunity to decide where you want to “cut” the track for your ringtone remembering that most phones divert to voicemail after 10-20 seconds
13. Click on GarageBand’s ruler on the point at which you want to start your ringtone
14. Select Edit from the menu bar and Split
15. Click anywhere in the grey area underneath your track, then click on the orange track to the left of the vertical red line
16. Select Edit from the menu bar and Delete, this will delete the portion of the song to the left of where you have just split it
17. Click and drag the remainder of the track all the way back to point zero on the GarageBand ruler
18. Press the GarageBand play button to decide where you want your ringtone to end and make a note of where that point is on the ruler
19. Press the GarageBand play button again to stop playback and click in the ruler at the point you made note of above
20. Select Edit from the menu bar and Split
21. Click anywhere in the grey area underneath your track, then click on the orange track to the right of the vertical red line
22. Select Edit from the menu bar and Delete, this will delete the portion of the song to the right of where you have just split it
23. Select Share from the menu bar and Send Song to iTunes
24. In the resulting pop-up window ensure that Compress Using is set to MP3 Encoder and click Share

iTunes will automatically take focus and start playing your ringtone. All you need to do now is send or copy your newly made MP3 file to your mobile phone and set it as your ringtone. Please note, you are not legally entitled to distribute your new ringtone to anyone else.