iPhone CarPlay text message audio routing is unpredictable

Cellular phone calls, SMS/iMessages, and internet-based messaging services such as WhatsApp do not necessarily behave in the same way when an iPhone is connected to a car's Bluetooth system and a Bluetooth headset.

The important distinction is that phone calls and message announcements are handled differently by iOS.

\- Incoming cellular calls: If your iPhone is connected to your car through Bluetooth or CarPlay, the call will generally be routed through the vehicle's audio system. You can answer and converse using the car's microphone and speakers. However, the actual audio route can depend on your iPhone's call audio settings and the connected devices.

\- Incoming text messages (SMS/iMessage): If you have enabled Announce Notifications and the relevant notification settings, Siri can announce incoming messages through supported devices, such as compatible headphones or CarPlay.

\- WhatsApp and other messaging apps: These are internet-based messaging services. Their notifications can also be announced by Siri, provided the app supports notifications and you have enabled the appropriate announcement settings.

\- Which device announces the message? This depends on several factors, including the active Bluetooth connection, whether CarPlay is being used, the connected audio devices, notification settings and iOS audio-routing behaviour. It is not necessarily determined by whether you are actively using your iPhone or whether its screen is locked.

For example, if you are listening to music through your car's infotainment system while wearing a Bluetooth headset, the announcement may be routed differently depending on which audio device iOS is using for that notification.

One important point: Simply connecting an iPhone to a car and a Bluetooth headset does not guarantee that Siri will announce messages through one particular device. The behaviour depends on device compatibility, connection priority and the notification announcement settings.

In short, cellular calls and message announcements follow different audio-routing mechanisms in iOS. It is therefore important not to assume that the device handling your phone calls will necessarily be the same device through which Siri announces your incoming messages.

What Call? On an iPhone, you can make and receive various types of calls. Here are the different types:

1. These are standard voice calls made over the cellular network. They utilize your carrier's voice network to connect you with other phone numbers. Allow phone calls on your iPad, iPod touch, and Mac
2. FaceTime Audio allows you to make voice calls over Wi-Fi or cellular data using your internet connection. It provides higher audio quality compared to traditional cellular calls.
3. FaceTime Video enables you to have video calls with other FaceTime users. It uses the front or rear camera on your iPhone to transmit live video during the call. Use FaceTime with your iPhone or iPad - Apple Support (IN)
4. VoIP (Voice over Internet Protocol) calls use internet connectivity to make phone calls. Apps like Skype, WhatsApp, Viber, and Google Hangouts utilize this technology, allowing you to make voice and video calls over the Internet.
5. Some carriers support Wi-Fi calling, which allows you to make and receive calls over a Wi-Fi network instead of relying solely on cellular coverage. This can be useful in areas with weak cellular reception. Make a call with Wi-Fi Calling - Apple Support (IN)
6. The App Store offers numerous calling apps that utilize different technologies. These apps can provide additional features and options for making calls, such as international calling, call recording, and more.

It's important to note that the availability of certain call types may depend on your iPhone model, iOS version, and carrier.