Will my iPhone use my data when connected to Wi-Fi?

I have an iPhone 3gs and was wondering, if my cellular data is turned on but I'm connected to Wi-Fi at home say, will the iPhone automatically use my Wi-Fi over my data?

No it's free Wi-Fi when your connected to anyone's Wi-Fi.

Nope!

Yes. All iPhones since the 1st have been set up that way.

No, the iPhone would only use your Wi-Fi. It should only use cellular data when you're not connected to a router.