That is not correct. My business had such a number in Konawa, Oklahoma, in the 1950-1952 and the calls were charged at the normal sent-paid station rate rather than as a collect call. (In Southwestern Bell territory they were called "Enterprise" calls rather than Zenith. Some states or companies called them "WX" numbers rather than Zenith or Enterprise.)
The advantage to the caller was that they did not have to go through the hassle of making a collect call. The advantage to the terminating business was that the call was charged at the sent-paid rate and the that callers who might be hesitant to make a collect call because they felt it would tab them as a cheapskate or for other reasons would not feel the same stigm.
A disadvantage was that a separate Enterprise (Zenith, WX) service had to be obtained for each city you wanted the receive such calls from. There was a monthly rate for each such service, which would add up quickly if you had such service from several originating cities.
I think 800 numbers started quite a bit before that. And having remote locations was not a big deal for airlines which had massive data lines already connecting their offices.
When 800 numbers first went in, airlines already had massive call centers. American Airlines call center was in a suburb of Fort Worth, while the huge computers already in existence were underground in Tulsa, where they remain to this day. Airlines had published (local) numbers in most cities they served, and often in surrounding cities, connecting by FX lines to their call centers. If you called the listed number for the airline, you reached the call center, not the local ticket office. The 800 number just made the call center available from everywhere in the country, not just in places where they had FXs. (It also was usually cheaper from a hotel.)
Wes Leatherock snipped-for-privacy@aol.com snipped-for-privacy@yahoo.com