Is it true that an iPhone without cellular service and is out of WiFi range can still be used to dial 911?

Yes. It’s not limited to iPhones either any mobile will work the same way as long as there’s cell signal. It won’t work in the middle of no where with no network coverage. I think in the US the phone doesn’t even need a sim inserted.

If it’s out of wifi range and out of cell service range (g range) no cell phone is going to work. That’s why many of our national parks still have pay phones.

As long as you are in range of a cell service your cell phone can call 911 even if you are not a subscriber to the service.

Edit: I found this website. It’s really good for 911 FAQ’s. https://www.911.gov/calling-911/frequently-asked-questions/

If there is a cell signal (your network or not), then 911 will go through,

But 3G is going away and some places it had ended.

So it needs to be 4G or later !

Any phone in general with or without WIFI or a phone company can contact 911.

Yep all phones have emergency 911 service even without a sim card.

No. It needs to have service. But 911 will go through on any service provider in the area.

This is good to know, too.
https://www.fcc.gov/sites/default/files/text-to-911_-_what_you_need_to_know.pdf

Thanks, everybody, for your replies!