Oh god, yes. I worked in a call centre for six months and it was dreadful. The combination of dealing with sometimes frustrating situations + the anonymity of a voice only call... People were regularly dreadful. Definitely at least 10% very rude people.

I also took it to be a sign of the 'banality of evil', that people having a nice time with their friends, eating some nice food, are generally pleasant. But put them in the privacy of their own home, speaking to a faceless stranger, and suddenly they can be awful. But I tried not to judge them to harshly. The design of call centres, with long hold times and staff with no real power to do anything helpful, is pretty much guaranteed to frustrate the most saintly of people.