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My wife and I are using key cards for her Model 3. Our phones (both Moto G5 plus) worked less than half the time. I tried some workarounds (toggling airplane mode or Bluetooth using an automation program) but had no luck fixing it. Decided it wasn't worth the hassle. I'm hoping they fix the issue or make fobs available but remaining patient while Tesla works on the problem.
I have an iPhone SE on iOS 10. Never got iOS 11 because of all the reported issues. The phone is my primary means of access. It works almost all the time. But I have to have the key card with me at all times because on rare occasions the phone doesn't work.