But THAT was when phones had cranks on the side. ;) 5 nines is a myth, conjured up by sales cretins to have something to sell...If I remember, 5 nines translates to 6 minutes outage a YEAR..? (Correct me if I'm wrong here) It's a marketing ploy for liar sales people and CEO's, it has absolutely NOTHING to do with real-world conditions.
BTW - One of my best friends growing up ( and we took EE together ) grandfather was the V.P. in charge of AT&T's LongLines division while a lot of the "wire was pulled". From what he said of his grandfather's remarks, they didn't think about five 9's. The question was how much spare/redundant capacity did you have, both for dependability and to support the countries growth. Not exactly "this quarter's profit" thinking -sigh-.