USSD API
The Windows USSD API is an abstraction of the underlying Unstructured Supplementary Service Data (USSD) protocol, which hides most of the details to simplify app development. This API enables mobile broadband apps to send USSD strings to a new or existing session or to cancel an existing session. This API supports notifications from the network that may or may not require a response. A response is required for a network-initiated USSD request or when further information is needed after a mobile-initiated operation.
For more info about the USSD API, see Windows.Networking.NetworkOperators namespace.