I have an iPhone 4, but have had this issue ever since my iPhone 3GS.
I don't use voice control. I don't like it. However, my iPhone case--a Belkin folio case which I love because it holds my credit cards and protects the screen--has a little lump over the spot where the home button is, so that every time I have my iPhone in my pocket and go to kneel down (or even if my pants are a little snug), it holds down the home button and triggers the voice control. This is so annoying, because I can be anywhere and my iPhone will just start playing music out loud.
How is there not an option in the General Settings to turn voice control off?! Is there any known way to turn it off? And I'm not talking about just putting a passcode on the phone, because that doesn't disable the voice-controlled iPod. I would LOVE to turn voice control off completely, so that I can keep my nifty case. Does anyone know of a way?