PhoneLineTransportDevice API no longer works on Windows 22H2

[BestOwl]

Recently I discovered that starting Windows 11 22H2 (build 22621), PhoneLineTransportDevice API no longer works, which resulted in our app's Calling feature no longer working.

The Calling feature currently relies on the PhoneLineTransportDevice API. The following is a brief description of how to use this API:

1. Enumerate a PhoneLineTransportDevice using either the DeviceWatcher or DeviceInformation.
2. Call PhoneLineTransportDevice.RegisterApp() to register the app with Windows for the associated PhoneLineTransportDevice.
3. Call PhoneLineTransportDevice.ConnectAsync().
4. Use PhoneLineWatcher to enumerate PhoneLine, similar to the DeviceWatcher.
5. Call PhoneLine.Dial()
   Note: Microsoft's Your Phone (now called Phone Link) uses the same mechanism to implement the Calling feature as of 2020, not sure for now.

However, after upgrading to Windows 11 22H2 (build 22621), calling PhoneLineTransportDevice.RegisterApp() either results in non-functional or throws a System.UnauthorizedAccessException, even though PhoneLineTransportDevice.RequestAccessAsync() returns "Allowed".

I tested Phone Link on my PC and verified that it works without any issues. Therefore, I am not sure why our app is experiencing this problem.

I am seeking assistance in resolving this issue. If the PhoneLineTransportDevice API is no longer usable, I am open to suggestions for alternative solutions.

[BestOwl]

Windows 10 22H2 also has this issue.

[BestOwl]

New discovery on Windows 11 22H2: In UWP apps, PhoneLineTransportDevice.RequestAccessAsync() now will always return "DeniedBySystem"

[BestOwl]

I made a small UWP app to test this API.
https://github.com/BestOwl/MyPhone.CallingDiagnosis.Pltd

Here are the test results:

OS	API status
Windows 11 22H2	❌ PhoneLineTransportDevice.RequestAccessAsync() return DeniedBySystem
Windows 10 22H2	❌ PhoneLineTransportDevice.ConnectAsync() return false, unable to connect
Windows 10 21H2	✅
Windows LTSC 2021	✅

[BestOwl]

Found this method in YourPhone.Calling.Managed.dll from the latest PhoneLink app:

public static unsafe bool TryUnlockPhoneLineTransportDeviceAPIs(IObjectReference _obj)

Seems like Microsoft blocks this API on purpose🤔.

[abusaadp]

Has Microsoft made an official announcement that Bluetooth calling will not work in Windows 11? Or have they changed the API for Bluetooth calling?

[abusaadp]

I contacted Microsoft and they said they were not aware of this issue. After checking they said there is some permission issue with this API in Windows 11 and they will resolve it soon. So we must wait for Microsoft to resolve this issue. Thats why this API is working for PhoneLink app as it may not have this permission issue.

[abusaadp]

Recently I got an email from Microsoft saying that this issue has been resolved but still the app is not working for me. The windows version has been updated to 23H2. Also even in the previous version of Windows namely 22H2 the bluetooth calling was working for the following apps.

1. Grid3 (https://thinksmartbox.com/product/grid-3/)
2. CallCenter (https://www.justremotephone.com/) and
3. Thy Phone (https://apps.microsoft.com/detail/thy-phone/9PKT9JS17KXZ?hl=en-us&gl=US)

So few of the apps bluetooth calling is working for 22H2 itself. Maybe there is some issue in our app.

[Manmenhongyi]

I have encountered such a problem. After compiling, packaging and installing, I can't make a phone call. When I press the dial key, the software will crash.😰

[Manmenhongyi]

I can't use the dial-up call function normally in Windows10 22H2 and Windows11 23H2.😩

[zhenbohuang]

@BestOwl

I try CallCenter (https://www.justremotephone.com/) and Intel Unison in 22H2, and both them worked fine.

And i find that both them pair the phone in app, but not from OS.
And if you pair the phone from OS firstly,
you need pair from the app again, or unpair from OS then pair again from the app before you can add the phone to the app.

Maybe it is the reason of why PhoneLineTransportDevice.RegisterApp() throws a System.UnauthorizedAccessException,
because the phone is NOT pair by the app, so the app do not have enough permission to link it?

[BestOwl]

@BestOwl

I try CallCenter (https://www.justremotephone.com/) and Intel Unison in 22H2, and both them worked fine.

And i find that both them pair the phone in app, but not from OS. And if you pair the phone from OS firstly, you need pair from the app again, or unpair from OS then pair again from the app before you can add the phone to the app.

Maybe it is the reason of why PhoneLineTransportDevice.RegisterApp() throws a System.UnauthorizedAccessException, because the phone is NOT pair by the app, so the app do not have enough permission to link it?

I tried paring the phone in-app, but still no luck.