once you have your service up you can create a project (it could be a web API) that calls it and then send it in REST
If you go for the webApi
add the service to your project, and in the controller inside the method do this:
yourService.yourMethodRequest request = new yourService.yourMethodRequest();
yourService.ServiceClient serv = new yourService.ServiceClient();
yourService.yourMethodResponse test = serv.yourMethod(request);
return View(test);
This will return it like json or XML to be call in REST
if you want to go for the WCF solution read this
Reusing WCF Service Across Several Applications using Different Bindings[
^]
Hope it helps