It doesn't have a sim. The Pebble's purpose-in-life was to be a good watch first. It complements your phone with smart features like notifications, automatically setting the time on your watch based on your phone, and syncing your calendar to Pebble's timeline. It's not a phone replacement like you're looking for, so Apple Watch is a good fit for you.
Still, I found my Pebble greatly reduced the time I spent looking at my phone because I didn't need to take my phone out of my pocket upon receiving a notification or to check the next item on my calendar.
Does Pebble have a sim? The biggest benefit of apple watch for me is that I can take it anywhere without my phone, play sports, shopping, running, the sim card in the phone is the best thing that keeps me away from staring at my phone screen while I am going out.