Where do ringtones go after I purchase them?

Did you buy the ringtone iphone directly from the iTunes store on your phone or via iTunes on your computer? Direct purchases in the mobile iTunes store are directly added to your ringtone library of the device (and it should have prompted you if you wanted to make it your default tone or assign it to a contact). Those purchased on iTunes or from other sources would have to be sync'ed with your iPhone in iTunes

 

just for clarification, ringtones that are purchased once from the iTunes Store don't fall under your purchases to download again. You literally need to sync the tones on iTunes so that they're saved because if they get erased from your phone somehow, you can't re-download them for free again.