Now comes the most important part: using the service! How you go about consuming a WCF service depends greatly on the type of client application used.
If you plan on calling a WCF service from a non-WCF client, then have no fear, you're still in great shape. One of the design goals of WCF (and any quality SOA solution) is interoperability, which means that a WCF services should be consumable on a wide variety of platforms and technology stacks.
Now, it is still the responsibility of the service designer to construct a service that's usable by non-WCF applications. For instance, a broadly used service would offer a basicHttpBinding to ensure that applications based on the .NET Framework 2.0, or JRE 1.4 would have no problem consuming it. An interoperable service would also use security schemes, which rely upon commonly available certificates for transport security.
Let's assume that a WCF service with a basic HTTP endpoint has been exposed. Let's also assume...