Create a promo video for our app functioning

Make a promo video for showing how our App functions. We have a calling app, what we need to show is how it functions. So here is what you need to demonstrate, After you register in our app, and you select a contact and click call button, once you click call button, what happens is you receive a incoming call and then you pick up that call, you hear a dial tone and then the person you want to call is called and then they both can talk. To simplify more, say der r two people, A and B, A wants to call B, A registers in app and places a call to B, what happens is.... A gets incoming call, he picks, B is dialed, B's screens see's a incoming call from A and he picks A and B can talk to each other. This is what you need to demonstrate by a video. You can create yr own script, select minimum possible time. You can use animations, voice over, white board, be creative, we should like it and it be professional. Please also share yr past work links in proposal.