Data Plan Ran Out - Error Messages

[bxhxdlsb]

That's the thing. I am connected to my home wifi router, and its showing the connection is good. When my data plan had some memory left, i was assuming that it was using the wifi for the internet explorer and for app downloads. But i guess it was using that 20mb at times. Because i have a home router, i thought nothing of the "data plan" because i knew the phone had wifi. however it doesnt seem it works that way.

specifically what im asking i guess is how to setup my phone to use strictly wifi, and also make the internet functions work on my phone when i have no data plan.

thanks for the reply