how to set so text/vm tone notification only plays once

i know this is a small thing, but sometimes it's the small things that irritate.... When someone sends me a text or phone message, my iphone 4 will make a notification tone, then, maybe 15- 20 seconds later, another. This is distracting, and downright annoying when i'm in a real live conversation with another person. I now catch myself "suspending animation" until the second tone sounds. I want the phone to sound an alert, but only once, not repeated. i can't see how to set it for this.... is there a way?

note: this is NOT the "stutter" issue that some people had with iOs 5.

this is a separate, distinct second notification for the same message.