i do not have international data plan. i will be travling to china.

Ting, it depends on where you use wifi service. Some areas like airports, hotels, restaurants and shopping malls provide free wifi service. If you go to these places, then you needn't pay. However, some hotels do charge a certain of money for providing wifi service. They usually charge by hour.

No matter wifi is free or not, you won't be charged on your phone bill.