Android Developer Needed – GSM + SIP Conference Calling in Default Dialer App

We have an Android mobile dialer application that is set as the default phone app. The app supports: GSM/SIM-based calling SIP/VoIP calling We need to implement a feature that allows conference calling between: One GSM call One SIP call Requirement When a GSM call is active and a SIP call is active, the user should be able to merge them into a single conference call so that all participants can talk together. Technical Expectations Experience with Android Telecom framework Experience working with: Connection Service In Call Service SIP stack (PJSIP or Android SIP API) Handling audio routing between GSM and SIP Managing call states and audio focus Proper call merge / conference implementation Clean and stable solution Important Notes The app is already functioning for individual GSM and SIP calls. We need proper audio bridging between GSM and SIP. Should work on modern Android versions (Android 11+ preferred). Deliverables Working conference implementation Source code integration Documentation of implementation Testing support Please share: Similar projects you have worked on Your experience with Android Telecom API Estimated timeline and cost

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