There was only one time it tried to work without a data plan, but that was an ATT Hotspot (at a starbucks), but I didn't have my ID/pswd of for my ATT DSL service at the time to try it further (only got to the login page).
The wifi logo remains gray until you have ATT activate the data plan, then it becomes blue and works. I believe that the Wifi is meant to only be a backup for the cellular data connection, when the cell signal is low or non-existant and there is a wireless signal available. Not sure if other carriers do this (so is it carrier specific OR device specific), or if unlocking it changes this.
I am really ticked off at BB and ATT because there is nothing in their advertising/prod. literature that says this. I wanted wifi without a data plan and now I'm stuck paying for the data plan. They are very misleading in their literature......apparently to increase data plan revenue.....this really sucks!!