How do you customize/change/add a ringtone on the NTT Docomo SH906i phone?

I currently just purchased the Docomo SH906i phone, and was wondering how to go about changing, or adding ringtones. I am aware that unless you are a Japanese resident, it is difficult to change your ringtone, though I am still curious as how to try. I have also heard that there may be need for a MicroSD card. Any help or information regarding this matter would be greatly appreciated! =)