(A couple of decade ago now - my memory might be inaccurate.)
You call the regional center (the 911, or in our case, 112 responders), you negotiate a timeframe for your tests (so that there's enough operators there), you tell them the phone number (and other data) that will be used for testing (because the responders get the approximate location of the caller, and might still send someone to check after a call, even if the voice doesn't get through), and then call 911 (112 here) a bunch of times.
Also, emergency calls have to work even without a sim card inserted, or with a simcard but still locked (via sim pin), or with an unlocked sim but locked screen, so that had to be tested too.
Somehow I manage to swipe the screen up and press the relatively small 'Emergency' button, all without touching the phone. It's really weird.
Admittedly this is roughly once every 2 years, but still I’m about at the point where I’d like to disable all automatic emergency services.
This resulted in the phone doing various things, such as opening the camera (double press of power), trying to turn itself off, and, worse: activating the "I'm in danger mode" (5 power presses in succession) and counting down to calling 911.
I caught it and cancelled before it dialed, then turned off the phone. However, as you might guess, the phone turned itself back on!
Fortunately I was able to (with much aggravation and accidental swaps to the camera app), eventually get to settings and disable the feature.
I had to do this because the kids discovered that if they held down power off and then slid the bar over a nice woman would talk to them and then a big truck would show up!
Came downstairs to hear them talking about calling 911 - when I picked up the phone there were four outgoing calls!
Fortunately the big truck did not show up, so I guess the operator was able to figure out that there was not actually an emergency (or maybe the phone was too old to communicate its location).
Cannot have FCC etc. uncertified phone connect to normal networks - that would be a mess.
I’m not aware of any western provider saying “oh, that block of IMEIs aren’t allowed to connect to the network”.
Canadian government shadow-banned sales of a bunch of Xiaomi cell phones, but local providers have no issues authing them onto the network. Can’t say no to that juicy roaming revenue even if it means putting your network at risk.
I don't think they'd block them from roaming if the device has a foreign network sim that's authorized to roam though. Of course, major US carriers basically don't allow their subscribers to roam to other major carriers.
I have a friend who used to work on cell towers and he'd need to do a test call after certain types of maintenance, and might visit a few towers a day to do that work. On the other hand, a particular phone model probably only needs one or two live test calls per firmware release, so there's probably a lot fewer of those calls overall, even if you're at a dispatch center that serves an area including people testing phones.