A friend told me this month about a startup founder who lost internet-based phone service during a power cut and could not call for an ambulance when his father collapsed. I have not been able to verify the specifics of that story, and I am not going to repeat it as fact. What I can verify is that the underlying vulnerability is entirely real, and it is one almost nobody using one of these services has actually thought through.
An ordinary wired telephone line carries its own power down the copper from the exchange. It rings during a blackout because the network, not your house, is supplying the electricity. Voice over IP has no equivalent. It needs your router, your modem, and often a separate adapter box, all drawing power from an outlet in your home, and the moment that outlet goes dark, so does your phone, at precisely the moment you are most likely to need one.
That is one problem, and it has an available fix, which is a battery backup for the networking equipment, a solution most subscribers do not know they need and were never told to buy.
The second problem is worse and does not have an available fix yet. Emergency dispatch depends on knowing where a call is coming from, and a landline’s number has always mapped to a fixed physical address on file with the phone company. An internet phone number maps to nothing physical. It is an account, associated with whatever address the subscriber typed into a form when they signed up, which is fine until the service travels with them to a different city, or a different flat, and nobody updates the record.
Regulators have required providers to at least ask subscribers to confirm their address, which is a start but not remotely the same as a system that actually knows where you are calling from the way the old network always did, without anyone having to remember anything.
None of this is an argument against the technology, which genuinely is cheaper and often clearer than what it is replacing. It is an argument for treating an internet phone as a second line rather than a full replacement until both gaps close, because the failure mode here isn’t a dropped call. It is nobody knowing you called at all.