If I have the KIN TWOm but do not have a data plan and there is free wi-fi somewhere, will I be charged?

If I'm sitting in a coffee shop and they have free wi-fi for customers to use, would I be able to open the internet free of charge for surfing? If so, what is the point of having a data plan then if this is possible? I'm currently looking for a new cellphone because my contract is up, and the KIN Two looks like a solid choice. This part is confusing me though, what gives? Thanks ahead of time for any help you can offer!