23. A human-machine interface telephone gateway as in claim 20 , wherein the audio voice command is an audio command to take action, the system command is an action request, the confirmation message contains a confirmation that the supervisory control and data acquisition system took the requested action and the audio message reports the confirmation.
20. A human-machine interface telephone gateway for providing a remote voice interface with a supervisory control and data acquisition system, comprising: a processor; an application programming interface with the supervisory control and data acquisition system; a data connection with a cloud telephone service; a non-transitory computer-usable medium having computer readable instructions stored thereon that, when executed by the processor, cause the processor to perform operations for voice communication with the supervisory control and data acquisition system, the operations comprising: receiving via the interface with the cloud telephone service a text command identifying an element of the supervisory control and data acquisition system and an action to be performed, the text command being derived from an audio voice command received by the cloud telephone service from a human operator; transmitting, via the application interface with the supervisory control and data acquisition system, a system command based on the text command, after receiving a text approval in response to an approval request via a conference call; receiving, via the application interface with the supervisory control and data acquisition system, a confirmation message in response to the system command; and transmitting, via the interface with the cloud telephone service, text for conversion to an audio message reporting the confirmation message to the human operator.