IPhone 4: Does using your Wi-Fi count as data?

I'm using my iPhone and I have my Wi-Fi on. If I'm online, is that just using the Wi-Fi or is that counting towards my data usage?

No it will bypass your data usage.

No, if your using Wi-Fi it does not affect your data.

No it will not I promise!

Data passes by two methods. Over the cellular network on 3G or over Wi-Fi. The dataplan is tied to 3G usage. If you are using Wi-Fi you are not using up your data plan usage.

No its not. Only 3G/4G does.