I don't remember exactly, but it wasn't like a switch someone threw. By the end of the 90's, while some people were getting pretty adept at dodging phone calls, you have to understand widespread adoption of cell phones, or even caller ID and certainly voicemail wasn't quite there yet, so landlines and answering machines still ruled. Having a separate number for the company was considered too expensive (although some did it), and later on, "signal ring", which gave you a 2nd number to the same line that made it ring different, became an option. It was still tough in a house with lots of kids, wife, etc to maintain radio silence. So calling people still resulted in "hits" for CS, and the company still had plenty of team players who had hired under the old way that were dedicated to the blue, so they'd just pick up. Failing that, they'd still send an agent out to meet a flight or have ramp control tell you to call them.

What really busted up the deal was 117, since you had to have prospective rest. When the other reasons popped up that allowed you to say no, they went a different way.