If we choose any Framework earlier than .NET Framework 3.0 while creating project or migrate an existing project from older version of Visual Studio, we might not find Add Service Reference in the context menu when you right click on the project. Here is a way to update to the framework version of the project and get Add Service Reference option in the context menu (Project should be saved before doing this) ,
Right click on the project and navigate to the following path,
Change the Framework version to .NET Framework 3.0 (or above)
Now we should be able to see Add Service Reference option!!!!!!