From the Q&A Support on Apple Watch Series 3 (GPS + LTE):
Apple Support Q&A said:
mactheman
Level 1 (8 points)
Apple Watch
Q:Apple watch series 3 incoming calls on LTE?
I am seeing that when both my Series 3 and iPhone are on LTE (no WiFi or BT) and someone calls me, only my iPhone rings. If I put my iPhone on airplane mode, then the Apple Watch rings. Never both.
Is this the way it is supposed to work?
Everything else is working perfectly. Outgoing calls, messages, email, etc...
Just incoming calls do not go to both devices when both are connected to LTE.
Posted on Oct 4, 2017 9:23 AM
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MoonJ.Oct 5, 2017 12:57 PM in response to mactheman
Community Specialists
Oct 5, 2017 12:57 PM in response to mactheman
Good afternoon mactheman,
Welcome to the Apple Support Communities!
Thanks for your question. The behavior you are experiencing is expected. Incoming calls will go to your iPhone unless it is turned off. If Handoff is enabled, you can send the call from your iPhone to your Apple Watch. But the incoming call will only go to the Apple Watch if the iPhone is turned off or in Airplane mode.
Use Continuity to connect your Mac, iPhone, iPad, iPod touch, and Apple Watch
Take care.