On an Orange Pay as you Go phone with WiFi is it free to use WiFi?

[pinker80]

i understand when i want to access the internet or built in apps like facebook twitter flickr myspace etc which connect to the internet i have to pay for mb's downloaded
but if i want to connect to my home WiFi or a free public WiFi network and use the phone's built in Opera mini browser is there a charge for it i've tried looking all over the orange site and can't find anything about wifi fees
if it helps i'm on an old choose your own off peak call plan and haven't gone on to one of the animal plans
thanks
i thought it was free but i've been charged for downloading gprs data and i haven't knowingly connected to the internet though on a couple of occasions i did forget to turn my WiFi on before opening up the Opera Mini Browser app