Disable Data Plan Features

[HotSauce]

Hey everyone. I just bought an HTC Touch Pro from Bell without a data plan, with the hopes that I would be able to use the Wi-Fi for internet instead. I want to be able to use the Wi-Fi to browse the internet, without having to pay for an expensive data plan. However, the data connection automatically turns on sometimes, and the SelfServe program has shown me that I have used some data already. I just want to pay for my phone services (minutes, texts, etc), and no additional charges. I've been using the internet browsers, the mail function, and the weather function.

My main question is, does anyone know how I can disable the data connection alltogether in order to avoid any additional charges?

And I'd also like to know which functions on the phone will result in the additional charges.

Thanks.