According to the article, whoever is behind this is using some web site that lets anybody with an email address spoof a US phone number to send fraudulent messages. The phone system badly needs to be upgraded so that people can't make calls or send text messages from somebody else's phone number. Doing that would not only stop the shady service that people are using to send these hoaxes to schools but would also stop the spam calls that come from people with the same first 6 digits as your number.

There aren't really legitimate use cases for phone number spoofing and even hiding your number so it shows up as unknown on caller ID is a good way to ensure the person you're calling won't answer the phone. When somebody makes a phone call, you should be able to trust that the caller ID shows the actual phone number that is calling you.