Using data plan when connected to wifi?

[djean]

Why is my phone logging data plan usage when I'm always connected to my wifi?  I'm seeing data usage every single day even when I know I haven't even left my house at all within a 24 hour period, or more?  My wifi signal is strong enough, no matter what area of my residence I'm in, and doesn't switch over to 3G.

[Ann154]

Do you leave your cellular data connection turned on while you are connected to wifi? The wifi radio has a sleep policy that can turn off the wifi radio when the phone is sitting idle. You can change the wifi sleep policy to never sleep under the advanced settings for wifi. The other option is to turn off the data connection (cellular 3G) when you want to ensure you don't send data over that path.

[djean]

Thank you for your reponse.  I'm sorry but I really don't understand except the part that I was able to find and went into the advanced wifi settings and changed it to Never sleep.  When I leave the house, or enter an area that I need 3G, will I then need to change it back?

Edited:  Ok I read about the "radio" part and understand it now.  Is there a good and hopefully free app that will automatically change it back when I need to go back to 3G?