If you want the watch to be able to answer calls when you're away from your phone, you'll pay a monthly device fee. The bluetooth will work with your phone if you don't need the watch to work without your phone nearby. I pay a fee to Verizon for two reasons.
1. I can take calls even when I don't have my phone on me.
2. I can listen to Spotify (streaming service) without my phone (great for use in the gym).