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SmartPhoneCTI

A CTI system for receiving an incoming call on your smartphone as a desktop notification on your PC. Clicking the notification opens a URL with the caller's number passed in (for example, a customer-management system).

How it works

sequenceDiagram
    participant A as Android app
    participant S as Relay server
    participant W as Windows resident app

    W->>S: Connect via SignalR and join a group
    Note over A: Detects an incoming call
    A->>S: POST /api/calls/incoming
    S->>W: Deliver the call over SignalR
    Note over W: Show a toast notification
    W->>W: On click, open the configured URL

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Only devices whose group ID and shared key match exchange notifications. A single server can serve multiple sites or teams.

Components

Project	Description	Target
src/SmartPhoneCti.Server	Server that relays incoming calls	.NET 10 / ASP.NET Core + SignalR
src/SmartPhoneCti.Desktop	Windows system-tray resident app	.NET 10 / Windows Forms
src/SmartPhoneCti.Android	Android app that detects and forwards calls	.NET 10 for Android (API 26+)

Requirements

• .NET 10 SDK

• The android workload to build the Android app

  dotnet workload install android

Try it

1. Start the server

dotnet run --project src/SmartPhoneCti.Server

It listens on http://localhost:5062. Open it in a browser to see the status.

2. Start the Windows app

dotnet run --project src/SmartPhoneCti.Desktop

It stays resident in the system tray. On first run the settings screen opens; enter:

Item	Description	Default
Server URL	Base URL of the relay server	http://localhost:5062
Group ID	The unit that shares notifications	1
Shared key	The group's passphrase; set it to the same value as the phone side	(empty)
URL to open on a call	{deviceId} and {tel} are replaced with the actual values	sample page

Settings are saved to %LOCALAPPDATA%\SmartPhoneCTI\settings.json. The tray icon is green when connected and red when disconnected.

3. Install the Android app

dotnet build src/SmartPhoneCti.Android -t:Run

Open the app, set the same group ID and shared key as the PC side, and tap "Start forwarding". When connecting from an emulator to a server on your machine, the server URL is http://10.0.2.2:5062 (the special address that points from the emulator to the host PC).

Checking it works

Even without an Android device, you can test the PC-side notification by posting an incoming call directly:

curl -X POST http://localhost:5062/api/calls/incoming -H "Content-Type: application/json" -d "{\"groupId\":1,\"accessKey\":\"your-key\",\"deviceId\":1,\"callerNumber\":\"0312345678\"}"

delivered returns the number of clients the call was delivered to.

API

Endpoint	Purpose
POST /api/calls/incoming	Notify an incoming call; the body has groupId / accessKey / deviceId / callerNumber
GET /api/health	Health check and current connection count
/hubs/incoming-call	The SignalR hub the desktop clients connect to
GET /sample/orders	Sample of the page opened when a notification is clicked

Operational notes

• Use a long, hard-to-guess shared key. Authentication relies on this key alone.
• Always serve over HTTPS in production. The app does not perform redirects, so enforce HTTPS at the reverse proxy or App Service level.
• The caller number is personal data. The server log masks all but the last four digits.

Constraints and known issues

• Call-log permission is required. On Android 10 and later, obtaining the caller number from the incoming-call broadcast requires READ_CALL_LOG. Distributing via Google Play requires a separate declaration for this permission (not needed if you build and install it yourself). A CallScreeningService approach that avoids this permission also exists, but it conflicts with spam-blocking apps, so it is not used (see the development notes for a comparison).
• Withheld (anonymous) calls cannot be forwarded, because the caller number is unavailable.
• Depending on Windows notification settings, the toast may not appear. If so, check that SmartPhoneCTI is allowed under Settings > System > Notifications.
• The URL to open on a call is a Windows-side setting; the Android side only notifies of the incoming call.

For developers

Use the scripts in tools/ to regenerate icons or capture screenshots of the settings screen. See tools/README.md for details.

License

MIT License