Thanks for stopping by the Apple Support Communities. I see from your post that you're considering purchasing an Apple Watch Series 4, but aren't sure whether you should get the GPS-only model, or opt for the GPS + Cellular model. I understand your specific concern is whether or not the GPS-only model will still function for calls and messages away from Wi-Fi, as long as your paired companion iPhone is nearby. I would be happy to provide you with some information!
Your Apple Watch communicates with your iPhone via Bluetooth and Wi-Fi. Having Wi-Fi on is necessary for some feature, but you can still use your Apple Watch without Wi-Fi for a lot of things. Calls and messages on a GPS-only model, for example, still work without Wi-Fi. Just make sure your iPhone is on, has a connection to your carrier's network, and Bluetooth is enabled. The Apple Support article About Bluetooth, Wi-Fi, and cellular on your Apple Watch - Apple Support expands how your Apple Watch connects:
To enjoy every feature on your Apple Watch, you need to turn on Wi-Fi and Bluetooth on your paired iPhone. Open Control Center on your iPhone, then make sure Wi-Fi and Bluetooth are on.
Your Apple Watch uses Wi-Fi and Bluetooth to communicate with your paired iPhone. If you have cellular, your watch can also stay connected through a cellular network. Your watch switches between these intelligently to choose the most power-efficient connection. Here's how:
- Your Apple Watch uses Bluetooth when your iPhone is near, which conserves power.
- If Bluetooth isn’t available, your Apple Watch will try to use Wi-Fi. For example, if compatible Wi-Fi is available and your iPhone isn't in Bluetooth range, your Apple Watch uses Wi-Fi.
- If Bluetooth and Wi-Fi aren't available, and you set up a cellular plan, cellular models of Apple Watch can connect to cellular networks.
In addition there are things you can do with your GPS-only model even when your iPhone is powered off or not around. You can read about what those things are here: How to use your Apple Watch without your iPhone nearby - Apple Support .
Enjoy your weekend!