You can use this watch with these 2 options:

1. WiFi Only: You can use Your Watch Free of charge to make calls/ text and internet apps etc As long as you are next to your Iphone (Using your Phones internet)
2. WiFi + Cellular: (For All major USA networks) In addition to above option to use it when you are next to your phone (for free), You Have the option to Add this to your cell phone plan (contact your provider to see what the fee would be) and then you can Leave your Phone at home and still use your watch to make calls/ text and internet apps etc