Set music for messages on iPhone 5?

Can I use music I have already purchased as my text msg notification? I want to be able to use existing songs that I have purchased on iTunes as my ringtone as well as message notification. Does the iPhone 5 allow this or do I have to purchase ringtones in iTunes?

1. Go onto iTunes and find the song
2. Right click on the song and select "get info"
3. Click on the "options" tab
4. Change the stop times to where you want your ringtone to play. It has to be under 30 seconds.
5. Go back to the iTunes library and right click, but this time on "create ACC version"
6. This will create a copy with the length and start and stop times where you want it.
8. Reset the start and stop times on the original.
9. Right click on the new version that you created and click "show in Windows Explorer"
10. This will take you to the song in Libraries. If you can't find it, type in the name in the search bar at the top.
11. Right click on the song in Libraries and click "rename."
12. Rename the extension from.m4a to.m4r (audio to ringtone). After you do this and click OK, a notice will come up asking if you want to do this. Click OK.
13. Sync up your iPhone. After you sync it, you can go into settings on your iPhone and then into sounds.
14. Go down the list and you can change whichever tone you want!