I need a straightforward, voice-only VoIP application that runs natively on both iOS and Android. The single, non-negotiable goal is crystal-clear voice calling: no video, no chat—just reliable audio communication every time the user hits the call button. Core scope • Native iOS (CallKit) and Android (ConnectionService) implementations • Secure registration/authentication, contact sync, call history, and push-based incoming-call alerts that display the platform’s standard call screen • SIP, WebRTC, or comparable stack—your choice—so long as it supports SRTP or DTLS-SRTP encryption and meets Apple and Google background-mode requirements • Source code must build cleanly in Xcode and Android Studio and be ready for App Store / Play submission =============Important !!!============== • User can select voice calling language in app and the voice should be translated to different language in real time Acceptance criteria • Calls connect in under two seconds on 4G or Wi-Fi • Packet-loss concealment and adaptive jitter buffering keep audio smooth at 15% loss • End-to-end encryption active by default • Push notifications wake the app and maintain call continuity even if the user swipes the app away • Delivery includes full source, build instructions, and a concise technical summary When you respond, focus on relevant experience—particularly any voice-calling apps you have already shipped, the codecs or SIP servers you used, and how you handled App Store / Play compliance for VoIP background modes.