I have extensive experience in developing server applications in C# (MS VS 2005/2008/2010) and Android apps for mobile authentication, product tracking and inventory management. As for these applications data is transferred between the mobile device and the server over the network via TCP/IP, I think much of the work needed to be finished for your project is quite similar to what I have done so far. Your mobile app I will create using Eclipse/Java. In a C# code I can do any required modifications.
All my mobile apps were tested and are working with the phones Samsung Galaxy S, Samsung Nexus S, Samsung Galaxy S II and with the Motorola Xoom tablet.
In your project description you do not specify anything about the lifecycle of the Android app and I assume it will be only up and running (so reachable from the C# code) only while the screen of the main activity of the app is the active screen on the mobile device, whether phone or tablet. That means it will be running as an activity, not as a Service and my bid is only valid for this case - a normal activity, not a service!