I wonder if it would really work. A ringtone that sounds like a sneeze.
If the sneeze sounds generic enough, it might fool anyone who wasn’t sitting in the immediate area.
Ring tones are one thing. But when you answer it, how are you gonna disguise your conversation as sniffles and coughs? 
It would only work if people used that as their ringtone all the time. I mean, if you remember to change your ringtone when you go to the opera, you could just remember to put the phone on vibrate.
It would still be rude, IMO. The only proper state for a cell phone in such a venue is either on vibrate (if you MUST have it on at all), or off. If neither is possible, then you stay home.
People still will want to beat the shit out of the ass that sneezed at a dramatic point.
Whle a sneeze is better than a ringtone, part of that comes from the fact that it’s involuntary. Someone who’s just faking a sneeze so his convenience is more important than my enjoyment of the performance I paid $120 for can go fuck himself.
–Cliffy