Changing number of ring tones | Phone/Device Issues and Features | Consumer forum

I'm trying to find a way to change the number of rings before going to voice mail, on my 7-Eleven Speak Out Nokia 2760.

7-Eleven and Nokia tell me it's not possible. Has anybody found a way to do it, or should I simply take their word for it and give up? I note that it's Rogers Voice Mail that Speak Out uses.