If you upgrade to iOS 5 and find that some of your ringtones are missing, here's what you need to do to get them back.
1. Open itunes and uncheck "sync ringtones."
2. Sync your iPhone.
3. Go back into iTunes and then check "sync ringtones" again.
4. Sync your iPhone again.
Your missing ringtones should now appear on your iPhone.
For more, see the original article at the link below.
Missing Ringtones After iOS 5 Update | Apple Toolbox