Unit Testing Methods that make WCF Service Call?

First attempt at any real unit testing. I have a WPF client application which receives data from methods in a WCF service. These method calls are made directly from my view models in the client app:

   public string LoadArticle()
    {
       MyServiceClient msc = new MyServiceClient();
       return Article = msc.GetArticle(_UserName);
    }

I then have a test project where I new up a viewmodel then call my method:

    [TestMethod]
    public void LoadArticleTestValid()
    {
        var articleViewModel = new ArticleViewModel("Thomas");

        string userName = "Thomas";
        string expected = "Article 1";

        var actual = articleViewModel.LoadArticle(userName); 

        etc.           
    }

Obviously this test will fail because the client application cannot reach the service to invoke LoadArticle. How is this situation tackled? Do I use Dependency Injection and pass a IMyService interface of some kind into the constructor instead of creating MyServiceClient in the ViewModel or do I mock the service somehow?