no sound on apps after receiving phone calls

[laurenfa]

When I am playing a game or using some other app on my iphone3g and receive a phone call and either decline the call or switch back to the app when I am finished with the call the sound does not work on the app anymore. When I come back to the app it is completely silent with no sound at all, even though I have it set to play all of the sounds, and double check this in the options of the game when I come back to the app. Am I doing something wrong, or is there something that can be done to fix this?
This happens with most (but not all) of my apps.

Thanks for any help/suggestions!