If you have ssh installed on iphone, you can use winscp (windows) or fugu (on mac) to access file system on iphone.
First, you should either use bosstools, or install cydia packager. Both of these apps will move your ringtones over to the accessible partition. Then locate the /ringtones/ folder on your phone (can't check right now, but i think it's under private/var/ringtones/). Upload your ringtones to this folder and you are good to go.