VOIP to local network calling App

We are seeking an experienced developer to create a user-friendly VoIP app and an accompanying robust VoIP framework. This solution will allow callers to make internet-based VoIP calls to recipients who lives in an area with out internet, that means the recipient will be using the local network to receive the call. the system has to ensure cost efficiency for the caller. The project requirements include: 1, VoIP Framework Development: Create a scalable and adaptable VoIP framework that facilitates internet-based VoIP calls from the caller to recipients connected via local network infrastructure. This framework should serve as the backend infrastructure for the app. 2, User-Friendly VoIP App: Develop a user-friendly mobile application for Android and iOS platforms that enables callers to initiate VoIP calls via the internet using standard VoIP protocols. The app should ensure a smooth user experience. 3, SIP Integration or Other Cost-Efficient Mechanisms: Integrate the VoIP app and framework with SIP or other cost-efficient mechanisms to ensure that the cost of calls for the caller is minimized. 4, Call Quality and Reliability: Ensure high-quality audio transmission and reliable calls within the framework and the app. 5, Security Measures: Implement strong security measures in both the app and framework to safeguard the privacy and integrity of voice calls. 6, Testing and Optimization: Thoroughly test and optimize both the VoIP app and framework for exceptional performance and user experience. This is crucial, especially in scenarios where the caller and recipient are on different network types.