If I didn't have my phone on vibrate and refused to have it ring out loud, I would get my son to play the Nokia theme on his fiddle and use that.
As soon as the grandchildren can talk, you can always get them to call out "Nanna - answer the phone!" or similar. You can record them and set them as ring tones.
My ringtone is Here Comes the Night, one of my favourites from when a teen in the sixties, it's loud and great. DH has Barcelona by Freddie Mercury and Montserrat Cabelle, also loud and beautiful, but he always looks around to see where music is coming from