We have a need for a simple VoIP application using PJSip, but implemented with Swift 3.1. The application should support IOS 10.3.1. The application should have a basic user interface that allows a user to make a voice call through an Asterisk PBX using the application. The application should implement CallKit. The User Interface should allow for dialling outbound calls, answering incoming calls, hanging up, volume control and blue tooth headset integration.