Upon first sync, iTunes 7.5 deletes iPhone ringtones transferred by iToner, a tool that lets you transfer your own MP3 or AAC audio files to the iPhone and use them as custom ringtones without hacking. The problem is easily solved by simply transferring the ringtones again with iToner.
According to Michael Simmons, Director of Marketing for Ambrosia:
"Just a heads up, iTunes 7.5 just came out, and it removes all of your custom ringtones when you connect your iPhone for the first time. If you resync again with iToner, then everything is fine (even subsequent syncs with iTunes is fine, it's just the initial connect of your iPhone that blows out the custom ringtones for some reason)."