Softphone SIP mobile app to connect with FreePBX / Elastix

I'm looking for someone who can create a mobile app which will work on Android and iPhone devices. It's a Visual softphone "one-click" to connect with a FreePBX / Elastix and make free calls direct to the PBX (VoIP). Basically, I would like an App that connects the end-user to my clients who have VoIP accounts in my FreePBX / Elastix server. The app must make direct calls between the end-user and my clients who have VoIP accounts in my FreePBX / Elastix server. The mobile app should update by a dashboard where the administrator will be able to do add new call-buttons and enter the server IP or domain name, enter the required credentials to make possible the app work with any FreePBX / Elastix server. The app must be a multi-language interface (Spanish, Portuguese, English, and Japanese). English is the default. All text translations will be sent to me and my team. The end-user should be able to hit "Call Now" button and he/she will not see the number calling. So in this case, the traditional keypad will be hidden and replaced by call buttons to dial. The Same app should have the ability to send messages in a chat with our staffs, including file attachments. I will provide same UI/UX screens during chat interview. You can suggest or program over any SDK or technology as Ionic, Ozeki SDK, webRTC, etc. Please quote me time, and cost for this project. It is an URGENT PROJECT! IMPORTANT: Full bid amount will be escrowed when the bidder is awarded, but not $1 will be released before the project is 100% fully functional, tested, and we are satisfied. We will NOT accept payments outside freelancer, so don't bother offering me a deal outside freelancer. If you don't agree to these terms/conditions, please don't bother bidding, as your bid will just get ignored and deleted.