Received call from this "PLANT TEST" phone number around 1357 CDT today on my GOOGLE VOICE number. Call was automatically BLOCKED by GV and put in the SPAM/JUNK CALLER folder. No message was left.

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Googling "Standard Plant Test Code suggests it is an "Automatic Announcement Circuit" type number (ANAC).
https://en.wikipedia.org/wiki/Automatic_number_announcement_circuit

"An automatic number announcement circuit (ANAC) is a component of a central office of a telephone company that provides a service to installation and service technicians to determine the telephone number of a line. The facility has a telephone number that may be called to listen to an automatic announcement that includes the caller's telephone number.

The ANAC number is useful primarily during the installation of landline telephones to quickly identify one of multiple lines."

Additional Information:
Location: Unknown City, TX, US
Service Provider: Standard Plant Test Code
Switch Name: PLANT TEST
Provider Type: Unknown
Phone Type: Landline/POTS/Broadband Testing
This reverse phone number was traced from the following IP addresses: None