Had same problem with my 3GS and now iPhone 4. When I am at the gym, using the included Apple ear buds with the remote/headset on them, it appears that the remote portion is not very well sealed, and all it takes is a little bit of perspiration, and all of a sudden my iphone starts acting all crazy, the music will pause on its own, or voice dialing will suddenly come on... Once it does that, I pretty much have to unplug the headphones and let them dry off. It's very natural when you are running or doing any other exercise that the little remote for the earbuds is going to rub up against your body and collect some perspiration. I'm surprised Apple didn't account for this when engineering the headphones and properly seal the enclosure for the remote, but I realize they are free/cheap and aren't meant to hold up too well to heavy use. I guess I'll just start using my old ipod headphones with no remote on it, although it is nice to be able to answer a call if I need to while working out.