Have a read through this Smurf. Have you checked settings or done the sound test by dialling #0# ? I would try these two options before trying any of the drastic measures. I feel sure it is in your personal settings menu.
Mcfluff I did an update a week ago and have standard ringtone. Nobody has phoned me today boo hoo but when I test it with my other phone it is ok so I will keep checking it. Thanks all x