I am looking for a developer to build a simple mobile-friendly web interface that allows users to place a phone call directly from their browser by pressing a single button. The user presses a **Call button**, the browser activates the microphone and speaker, and the system connects the user to a predefined phone number using the Twilio Voice API. The destination phone number must remain hidden and handled securely on the backend. When the call ends or the user disconnects, the page should automatically redirect the user to a URL that we provide (for example our company homepage). This project is intended to be a **simple MVP prototype**, not a full telephony system. --- Core Features Single Call Button Interface * One large “Call” button * No dial pad * Simple, clean interface * Mobile-friendly and responsive Browser Calling * Users must be able to call directly from their browser * Must use the user’s microphone and speaker * Must work on modern browsers Fixed Destination Number * All calls connect to one predefined phone number * The phone number must never be visible in the frontend code Twilio Integration * Use the Twilio Voice API * Implement secure server-side token generation * Handle call connection and disconnection events Call End Redirect * When the call ends or the user hangs up, the page should automatically redirect to a provided URL --- Mobile Compatibility (Important) The interface must work properly on mobile devices including: * iPhone browsers * Android browsers The developer should ensure correct handling of: * microphone permission requests * WebRTC audio playback * user interaction requirements for initiating calls Testing on both desktop and mobile browsers is required. --- Preferred Technology Frontend * HTML * CSS * JavaScript Backend * Node.js, Python, or similar server for Twilio authentication --- Deliverables * Fully functional web interface * Twilio voice integration * Secure backend for call routing * Automatic redirect after call completion * Instructions for deployment and configuration --- To Apply Please include: 1. Experience with Twilio or WebRTC browser calling 2. Examples of similar projects if available 3. Estimated cost and timeline Please start your proposal with the word **CALLBUTTON** so I know you have read the full description.