Correct me if I'm wrong, but I think I've read somewhere that it can be a SIM-less phone that abuses emergency call flow in 3GPP. GSM specs have special accomodations for 911/112 type calls that don't require a SIM(that sometimes ironically lead to normal calls working fine and just emergency calls failing).
Yes, you don't (in most countries) need a SIM for 112/911, and even when you do have one, you are allowed to use other carriers for such calls, even when you ordinarily shouldn't be able to roam onto them.
The specs do have that, but I used to work at a major mobile telco which didn't implement that part of the spec. The argument was that people would use emergency calls to test phones without a SIM. That may well have changed, but you can't assume that the spec will always be implemented in the network.
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