A data plan is mean you will be paying for data transmitted to
and from your iphone. If you play a song on iphone through a web
browser, it's worth about <3.5 MB data on 3G or FREE on
wifi.
If you buy an iphone without contract, you still can use the
phone to surf internet, but it'll cost more expensive as reflected
on bills as 3G data (for post-paid users without data plan). The
'data plan' is a discounted package for you so that you can surf
internet on the go with much fear it burst your pocket.
I am not too sure if pre-paid SIM can surf internet on iphone or
not.... If you're is post-paid plan (without data plan), it's
definitely going to be a huge bill if you do not have data
plan.
