You would have dialed "0" for operator, and the operator would have dispatched the emergency call.
If you have a traditional wireline phone, you do exactly what you do if the power is not out; the telephone system is independent from commercial power generation in this regard (power is supplied by batteries at the central office; that's why it's 48VDC).
Voice over IP is not "a little less reliable"; it's enormously less reliable. Despite this, I have Vonage service at my home; but, having worked in telephony for a long time, I understand the risks. One ought not minimize them for others who have less technical knowledge.
Thor Lancelot Simon snipped-for-privacy@rek.tjls.com
"We cannot usually in social life pursue a single value or a single moral aim, untroubled by the need to compromise with others." - H.L.A. Hart