All government numbers will begin with 1. Each county will be given a county code which will be a 2 digit number, and based on the demographic size I note in another domain?, there would likely be 65 counties. 00 will be the national government. All government numbers will begin with 1 + county code. National government will then be 100 for the first 3 digits of their telephone number. The 23rd county will be given 123 as their first 3 digits.
Unless previous arrangements were verified by both parties, the government will never call you and ask for your GIN. While there will be a push of better identification of scam calls, the system is not perfect. With that said, you might receive an automated message to call “particular agency” at “telephone number”, but the government will never make an unexpected call asking for your GIN. This is designed in such a way to protect the GIN holder. The last thing you would want is your GIN to get in the hands of a bad actor even if you have 2FA? on. Your GIN could still be sold, and might cause problems down the road.