We are trying to build a webapp for videochat that will run in a browser across platforms (desktop, iOS, Android).
At this time we are not aware of how to run webRTC
Update as of June 2017: WebRTC and getUserMedia are available in WebKit since iOS 11.
See also: Release notes from Safari 11.0
New in Safari 11.0 – Support for real-time communication using WebRTC.
New in Safari 11.0 – Camera and microphone access. Added support for the Media Capture API. Added ability for websites to access camera and microphone streams from a user's device (user permission is required.)