according to their customer services they dont charge anything for online use. u do have to pay one time online fee of 150rs but its one time only. all this applies when u get wiz internet card but if u get simple wiz card u have to pay 100rs everytime u make an online transaction.
i recently got wiz internet card and waiting for nadra verification. they told me it will take 3 days but its been a week
before that i had wiz card and i had to pay 100rs everytime i made an online transaction.