On the SD card, make a folder named mp3. In that folder make a folder named ringtones. (You can also make alarms and notifications.) Put the ringtones in there. They should show up in your ringtones list. (The phone will have to scan the SD card to see the new ringtones you put in there, so either set it to use the SD card externally [so a computer can read it], then set it back to normal, which forces a rescan, or just restart the phone.)