There exists a single instance of an SMS service which is both "Global" (not Realm and Global) and a Collection. This is the new-for-7.0.0 CorsService. This service operates as expected, however it does not render a UI entry. This is likely an oversight of the development of the SMS framework.
Install AM, look for the CorsService in the interface, it doesn't exist. You can however communicate with the REST endpoints and the service(s) generated execute as expected.