YES you can do ringtones. I've added a bunch. There is a specific way. I only know it for macs. I use Quick Time Pro. You can also use GarageBand and ITunes.
The phone does not accept mp3. However, if you create a m4p and rename it to a m4a, then the phone will accept and add to ringers. There is a website where I found how to do it, but it's bookmarked at home