When I am using my iphone at home for data how do I select that I want my data from my home wifi and not from the 3g radio? I don't want to use my 3g data allowance when I have wifi available.
Another thing you could do is to put it in airplane mode by going into settings. You also need to turn Wi-Fi back on after putting it in airplane mode.
But you should be fine by just connecting to Wi-Fi.