What’s the difference between GPS and GPS + Cellular?
GPS
Apple Watch Series 3 (GPS) lets you send and receive text messages, answer phone calls, and receive notifications when it’s connected to your iPhone via Bluetooth and Wi-Fi. The built-in GPS works independently of your iPhone for distance, pace, and route mapping in workouts.
GPS + Cellular
Apple Watch Series 3 (GPS + Cellular) has all the same features, as well as built-in cellular. It gives you the freedom to send and receive text messages, answer phone calls, and receive notifications even when you don’t have your iPhone with you.
Cellular Carrier Support
Connecting Apple Watch to a cellular network requires the same carrier as your iPhone, and we’re adding carriers all the time. If your current carrier does not support Apple Watch, cellular functionality won’t work until support is provided.
It can connect to your iPhone when itʼs nearby, a previously joined Wi-Fi network, or cellular. Your Apple Watch can connect to LTE networks. ... The Cellular button turns white when your cellular plan is active, but your watch is connected to your iPhone using Bluetooth or Wi-Fi.Jan 11, 2018