Our simulated ultrasonic sensor implements "analog sensor" generic service contract. If you want to make a service that communicates with the simulated ultrasonic service, just add a partner "analog sensor" (in RoboticCommons.Proxy.dll, mode information here http://msdn.microsoft.com/en-us/library/dd145244.aspx
) and bind your service with the simulated one with a manifest. With a generic partner, your service will be able to communicate with a real ultrasonic sensor too.
You should also take a look to the manifests included in the NXT-MSRDS pack (under "Microsoft Robotics Dev Studio 2008 R2\SimplySim\NXT-MSRDS\Manifests) to see how simulated service is created. All simulated services have the simulation entity name has partner. So you may have to change this name with your robot's name.