Using internet on orange Iphone

[BobbyBobBob]

I am currently in a contract with orange which consists of unlimited texts, 400 minutes and 80 mb of internet per month for so much money. I have recently bought an iphone and am now using that. I have noticed that even when going on the internet using wi fi it still eats away at the 80 mb. Does anybody know why this happens.? Also I know you can buy unlimited internet on for an extra £5 on other networks, is this the case with orange too?

Many thanks

[Milvus]

With a sim only contract on O2. you get 300 mins, unlimited texts, unlimited mobile date and unlimited wifi data... for £15 per month