Billing in the UK...I don't understand please help.

Hi all,
I recently upgraded from an 8100 to 8120 so I could benefit from the WIFI, thinking that when at home or at the office any emails or app notifications like Facebook would be free as it's working via the wifi.

I've been checking my Vodafone bills and there is little to no difference to the charges between the 8100 and the 8120 which doesn't really make sense to me.

Also, on the bill Data is logged as BLACKBERRY, which make me think it's all going via the carrier as there are lots of them....can someone please explain this all to me. Thank you folks.