is wifi free to use on my iphone?

[Mike]

hi i have an iphone on o2 payandgo does it cost me to use wifi as i had 17pound on my phone and now it gone i spoke to o2 and they say it cost to go on there but surely if u pay for your wifi you shouldnt ave to pay for it on your phone again lot of people told me it free are o2 mugging me off or is it true that you have to pay please let me no if eny one got payandgo phone and have had this problem or no the anser. thanks