Does it cost to use mobile data

Your cellular carrier charges for using mobile data. Depending on the plan you have you buy a certain amount of data, and when you use it up you pay for more. I can't be more specific, because there are several hundred cellular carriers that support the iPhone, and each of them has different plans. So the best thing for you to do is to call your carrier and ask, or log in to your carrier's web site and review your account.

Then obviously whenever you use data it is deducted from you balance, same as a call. Again this depends on what type PAYG plan you have. Some give you X days of data, some X GB. Check with your carrier.

With almost any carrier, you have either unlimited or limited data to your account. Call your operator and ask about your plan: how much data is included per month and how much it costs to exceed that amount

If I may be cruel: didn't you know what you signed up for and agreed to pay for?

Sagz3 wrote:

I was wondering whether it costs money to use mobile data

Considering the fact that you pay for a data plan every month, what do think the answer to your question is? Honestly...