If you have a Bluetooth speaker with an internal microphone, then it can indeed make and answer calls for you. In fact, if you Call Audio Routing is set to "Automatic" on your iPhone (which it is by default), it'll always go straight to the speaker. If you'd rather that not happen, here's how to change it.
How to change Call Audio Routing
- Launch Settings from your Home screen.
- Tap General.
- Scroll down and tap Call Audio Routing.
Tap either Speaker or Bluetooth Headset. If you tap Speaker, it'll automatically route to the iPhone's speakerphone.
So far, there is no way to automatically route things to the iPhone's earpiece, so you'll have to settle for speakerphone and then tap the button to turn it off every time.
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