Need voip application with grandstream API integration (only bid if you have working demo for test)

I am in need of an experienced developer to create a state-of-the-art VoIP application, with integration of Grandstream API. The platform should encompass advanced features, including:

- Audio/Video communications
- Instant Messaging with file sharing
- IP phone system

In terms of design aesthetics, I'm envisioning a professional yet minimalistic look -- Kindly keep the color scheme mainly in black & white to fit the business-oriented vision.

Having experience in VoIP applications and Grandstream integration is a must. The project holds an urgency so freelancers with ready demos for testing are given preference. Don't bid if you can't provide a demo for the test as we need to launch is in fast turnaround. Let's create a robust and user-friendly VoIP application together!