IM Chat and Voice Application for iOS, Android and Windows -- 2

We need someone whose working hours are US Eastern Time normal business hours (9 AM to 6 PM). Main requirements: - Individual & Group Chat (Text & Files): App user to/from app user; App user to/from non-user (via third-party SMS/MMS API) - Back-end Server & API: To retrieve recorded communications (chat and voice) stored on app server into our customer admin console - Voice Calling: App user to/from app user; App user to/from non-user - Complete installation instructions for the whole system for an on-premises setup. For communication between app users and non-users we would need each app user to have a virtual number. We have accounts for third-party APIs to create virtual numbers OR we can get whatever you recommend. The first deliverable would be the back-end server package and an iOS client app plus source code for both. Once that is completed, we would need an Android app followed by a Windows Phone app. Details are listed in attached file.