How to get Wi-Fi on my iPhone 4 anywhere without paying for the data plan?

I have recently purchased an iPhone 4 for at&t but got it unlocked and am currently using it for T-mobile. I have a 3g sim card so I'm using the phone as 3g anyway i have the Wi-Fi set up at my house and places like McDonalds and what not. But i was wondering if there was any way I could get Wi-Fi wherever I go whithout paying for the data plan?

So you're asking if there's a way to get the data plan on the phone without paying for it?

Yeah, have someone else pay for it >_>

The only answer is no for these reasons:

Data and Wi-Fi are two different connections, but they deliver the same thing.

The data connection on your phone is used with antennas all around your town and only communicates with those antennas in order to provide you with phone calls, voice, text, data, etc.

Wi-Fi, also known as WLAN(Wireless Local Area Network), only extends as far as your access point broadcast. Your access point is your router.

Unless there's an access point broadcasing a Wi-Fi signal everywhere you go, you can't get "internet" on your phone with out resorting to data, that's what it's there for.