Apple's iPhone requires files to be saved in the .m4r format to be synced and used as ringtones. Although iTunes does not have an interface designed specifically for the creation of ringtones, you can use the program in conjunction with tools native to your operating system to format any song or audio file in your library to create an .m4r file that you can use as a ringtone on your iPhone.
Select the iTunes file you want to convert to an iPhone ringtone from your iTunes Music library.
Right-click on the file and choose "Get Info" from the fly-out menu that appears. Click the "Options" tab in the resulting menu. Enter the time in the song you want your ringtone to begin in the Start Time field, and enter the time you want the ringtone to end in the Stop Time field. Both fields should be checked after you adjust the times. Make sure the range of times you entered is no more than 40 seconds. Click "OK."
Select "Edit," "Preferences" from the menu bar across the top of the screen. Make sure you are in the "General" portion of the "Preferences" menu and click "Import Settings." Make sure the "Import Using" menu is set to "AAC Encoder" and click "OK."
Right-click the file you want to convert once again, but this time select the "Create AAC Version" option in the fly-out menu. ITunes creates an AAC copy of only the part of the file you specified in Step 2 just below the original file. Right-click the copy and select "Show in Windows Explorer" from the menu.
Right-click on the file in Windows Explorer and select "Rename." Edit the file extension so that it reads ".m4r" as opposed to ".m4a."
Go back into iTunes. Select the AAC copy you created in Step 4 if it is not already selected. Press the "Delete" key. Click "Remove" on the first dialog box that follows and "Keep File" in the second one. Go back to the explorer. Click and drag the ".m4r" file anywhere in the iTunes window. It is now found in the Ringtones section in the source palette at the left of iTunes. You can add it to your iPhone whenever you want by connecting your iPhone to your computer and dragging the ringtone to the icon for the phone under "Devices" in the source palette.
- You can set the ringtone as your default on iPhone by tapping "Settings," "Sounds," "Ringtone" and tapping the file under the "Custom" section.