AFAIK there is no native Qt support for WCF or extensions; however, since you know that WCF can consume and expose a web service (in addition to WCF or a remote service, etc.), you only need to open the web service for another .NET application.
But this causes an interesting aspect; usually you should write a windows service (I suppose you are on windows) that displays as a web service, not through Qt. Qt is not perfect as it is a graphical interface (and very good); You will find yourself in several interesting situations: discussed here . It is usually easier to use a web service with Qt, as shown in this example .
Do you have the opportunity to open your service using another stack, such as ASP.NET or WCF or Java?