Android/iPhone SIP Dialer with source code using Xamarin Forms

I have a VoIP platform for which I need an Android & iOS app (phone/tablet) based on the latest version of CSipSimple that you can reference for the overall design using Xamarin Forms. This should support all version of Android, iPhone The app should integrate with the platform I built pull/push data via a REST API. The main functions of the app will include: 1. Making & Receiving VoIP Calls Over 3G/4G, WiFi, GPRS 2. Should not kill the battery of the mobile device 3. Address Book Integration with local Phone Address Book AND the platform 4. User Credentials Save / Change Username & Password 5. Volume Control 6. Protocol SIP (RFC 3261) 7. Media Support RTP (Real Time Transport Protocol) & RTCP (RTP Control Protocol) 8. Transport Mode TCP, User Datagram Protocol (UDP), TCP to UDP Interworking 9. Codecs G.723, G.729, AMR (Adaptive Multi-Rate Compression), iLBC, G.711, GSM. 10. Network Address Translation (NAT) Traversal Through Encryption & STUN 11. Voice Quality Silence Suppression, Packets Loss Management 12. DTMF - (Dual Tone Multifrequency) Generation & Detection (RFC 2833) 13. Call Status Indicator Displayed on phone screen 14. Call History, Call Detail Records 15. Speakerphone 16. SMS (through the platform) 17. App will be in English. 18. App should voice and SMS encryption The app will be marketed on the Google Market/Play and on iTunes, so it should be designed to those specifications. I would prefer someone that has an "innovative point of view". The VoIP platform and business was designed and conceptualized to allow for multiple SIP phone types to be connected to it and perform different things. The intent here is to find a good developer to build this first project and build more in the future. NOTE: There will be a focus on front end design clarity (which should be easy because we are using the other VoIP phone as a reference) but the code needs to be clean and error free (I can help test the apps). If you are not a strong developer that can put out well documented code that can be built upon, please do not bid.