iPhone ringtones appear to take the format of "m4r", which isn't a problem if you have garageband.
Making an iPhone ringtone isn't really much of a problem at all.
Here's a set of detailed instructions I followed some time ago to make a few ringtones for the Lady Elf (and the instructions actually make it look far more complex than it is in reality!):
To create simple, free iPhone ringtones from your iTunes library, follow these steps:
• Note: This process works with MP3, ACC, and AIFF files.
• Note: Only DRM-free songs can be used with this ringtone creation process.
o Any song downloaded from iTunes Music Store will have DRM (Digital Rights Management), so don’t use those songs.
o Any song ripped from a CD or downloaded from DRM-free sources (P2P, Amazon, your friend) will work just fine.
1. Fire up iTunes 8
2. Find the song you’d like to turn in to a ringtone
Select the song you want to use as your iPhone ringtone
3. Right click on the song
o Select “Get Info”
4. Hit the “Options” tab
5. Check both the “Start Time” and “End Time” boxes
Customize the start and end times for your ringtone clip
6. Specify what time interval you’d like to use as your ringtone clip (Make sure your ringtone is 30 seconds or less!!)
7. Click “OK”
o Make sure the song you want is still highlighted
8. Click on “Advanced” in your menu bar
9. Select “Create AAC Version” or “Create Apple Lossless Version” (Make sure your iTunes “Import Settings” are set to “AAC” or “Apple Lossless” and not “MP3″)
You want to create a duplicate song file with the customized playing time
10. A duplicate copy of your song will appear in iTunes – this new song will have the same filename but shorter “Time”
o Go back to the original song and uncheck those “Start Time” and “End Time” boxes
See the duplicate song underneath the original song?
11. Drag the duplicate song to your Desktop
Duplicate song file on Desktop
12. Once the duplicate song is copied to your Desktop, delete the duplicate file in iTunes
Notice that the duplicate song file is gone - deleted
13. On your Desktop, rename the file with the “.m4r” file extension – Use the new extension
o This turns your song file into an iPhone ringtone file
Use the new filename extension
The .m4r file is now a ringtone file
14. Your “songname.m4a” file should now be named “songname.m4r”
15. Drag the newly renamed .m4r (songname.m4r) file back into iTunes
16. Drag the file over the “Library” column and release when “Library” becomes highlighted
o You have to delete the duplicate song file (Step 12) otherwise iTunes won’t import your new .m4r file
17. You should see your new ringtone under “Ringtones” in iTunes
18. Sync your iPhone to get jiggy with your new iPhone ringtones!
An Eagle for an Emperor, A Kestrel for a Knave.