Question

Suppose I have a wcf service listening on a remote server.
Could a client, before connecting, know what port will be assigned by the operating system?

Answer 1

No, not by default… however you can wrestle control away by using the BindIPEndPointDelegate property of the ServicePoint managing requests to that uri:

var servicePoint=ServicePointManager.FindServicePoint(myServiceUri);
servicePoint.BindIPEndPointDelegate = (sp, remoteEndPoint, retryCount) =>
    new IPEndPoint(localEndpointDetailsGoHere)

You’ll need to manage ports yourself in this case.