Here are more docs on the 710 area code via a simple Google: https://www.google.com/search?q=%22710-NCS-GETS%22+card+ext:...

For example, this PDF explains a lot than anything present on HN or Wikipedia: http://chicagofirstdocs.org/resources/060912-GETS.pdf

Here's a doc that covers all US Federal emergency communications: https://www.dhs.gov/sites/default/files/publications/nifog-v...