With the Sept. 2010 release of iTunes 10, Apple removed the ability to create custom ringtones from iTunes. This article applies only to versions earlier than 10. Ringtones may still be purchased via iOS apps at the App Store or made in audio editing programs.
One way to check for what songs can be made into iPhone ringtones is by using your Purchased list. The Purchased list is a playlist stored just under the iTunes Store icon in the left-hand column of iTunes. It lists all the songs (and other media) that you’ve bought from the iTunes Store.
Some of the songs, though not all yet, in this list can be made into ringtones. Here’s how to find out which ones are eligble.