Wi-Fi instead of data on the IPhone 4?

I was considering getting the iphone 4 and I just wanted to know… If I have Wi-Fi in my house, can I use that instead of data? I'm pretty sure the answers yes, but I'm not very technologically advanced.

Yes you can switch forth between the Wi-Fi usage and the 'mobile network' usage, this can all be done in the settings. You can switch your data off at anytime so that you don't get charged extra.
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Yes you can. Just make sure you turn off the 3G data settings and turn the Wi-Fi on so you won't see a 3G at the top on the status bar and you will see the Wi-Fi signal on it.

Yes you could.