Connecting existing apps is simple to do. We can add a Connected Service for Visual Studio 2013 solutions and we need to install the Windows Azure Mobile Services SDK NuGet package for Visual Studio 2012, or you can download the source from the following link: https://github.com/WindowsAzure/azure-mobile-services. As you can see, the SDK is open source and hosted on GitHub rather than CodePlex which is the usual place Microsoft host SDKs. So, it shows that they're really building a cross-platform service here.
To connect to a service, follow these instructions: