This is indeed very common. Even in cities where they still have brick and mortar call centers, like Houston, they have remote agents as well. They have a lot of them in Utah, which follows the model companies like jetBlue and Marriott have used for some time, where mothers with large families work while being able to stay at home. One agent told me that they have agents in almost every state - some just 2-3 in one state.

I think a lot of CO's off-hours agents are these work at home types.

As for UA, I don't think they have any at home agents. Their remotes are ICC and it seems like they have some working out of Manila now as well. Domestic agents, who provide 100% cover for 1K and GS and varying degrees of cover for other elites, are in Chicago, Detroit and Honolulu. Detroit used to be exclusively or near exclusively for GS, but now cover 1Ks a lot. Honolulu tends to be the off-hour call center.