Question
How can I select a specific audio device before placing a call on my iPhone, without setting a new default device?
Background
During a call, I can route the audio to several different devices – my iPhone's speakerphone, various Bluetooth devices, iMac, MacBook Pro, etc. This works well when switching devices during the call. I can also easily answer a call from any of these devices.
However, I cannot figure out how to select another device before placing a new call, and just for that call.
Use Cases
My most common use case is when I'm already listening to audio on my iMac or MBP with (wired) headphones and need to place a call that requires me to continue using the headphones connected to the computer.
If I place the call first and then switch the audio to the computer, the other party often answers before the switch completes, and I've missed the first part of the conversation.
Same thing if my phone is mounted and/or charging and I want to place a speakerphone call – if I don't switch the audio before the other party answers, I'm left with an awkward hello…
Context
I'm normally using an iPhone XS with iOS 14 or an iPhone 7 with iOS 13. I don't want to switch the default device since there are many times I'd prefer to initiate the call normally, i.e. phone-to-ear.
Best Answer
Before placing the call, you can open Control Center and tap the AirPlay icon to select a Bluetooth destination such as for example a pir of AirPods. The following call will then use that audio device by default.
After the call is done, you'll probably to tap the AirPlay icon again to choose iPhone as your destination.
If you want to use wired headphones, you'll obviously need to actually connect them to the phone before they can be used.
There are no other settings or functionality for doing a once-only rerouting of phone-only audio to a specific device before placing a call.
There is however a different way to overcome the problem that the calls connects before you have managed to switch the audio destination: You can add a pause or wait to the actual phone number.
I.e. when you edit a contact on your phone, you can set their phone number. If you click the button labelled "+*#" you get the option to place a pause or a wait. Add this to the start of the number, and you'll get additional time to switch the audio destination.
A pause is literally just a pause for 2-3 seconds (afair), whereas wait means that the phone does not dial the rest of the number until you have tapped the phone to acknowledge.