I worked at 2.
The first one was for medicare insurance, inbound calls. I worked 2nd shft (3-11), and doctor's offices closed around 5 and old people be going to bed early. So like around 6pm, it was a breeze, get like 1 call per hour (damn west coast callers). Rest of the time I'm on the internet, texting, or chopping it up with co-workers, reading a book. Got promoted to QA 6 months, easiest job in the world

. Everybody smashing each other (I put it down with a few co-workers), but that caused drama. Seen arguments and fights between females in the building. People drinking and smoking weed on lunch break.
One lady, who was all in the church, was walked out by the FBI because she was scamming old folks for their credit cards (stole over 100k), but that was at her previous job. Quite a few dykes their. One with no experience whatsoever got promoted to supervisor, then manager, because she turned out the HR lady. Overall it was cool, but I couldn't see myself doing that forever, so I went back to school. I remember right before I left, they started mass firing people, for every little mistake. No show for work, fired, gave out wrong information, fired, ignored a call, fired, texting while working, fired, on the internet while working fired. I talked to one of the managers of fb and she was like I was about a month away from becoming the manager of QA. Said they would love to have me back.
Second one was a summer job while I was in school. AT&T call center, inbound calls. Worse job I ever had. I worked 2nd shift on that job too, but the calls never stopped. From the moment you log on until I get off, people calling in, complaing about bills or their iphone not working right. Every caller is angry and cursing you out. Supervisors stopping you from taking lunch or going on break because there are too many calls in que. I dreaded going in to work.

I was so happy to be leaving their and going back to school. The hiring manager was like I can come back anytime.

She probably thought different if they really listened to my calls, I was giving away so much free stuff (minutes, knocking money off people's bills, etc). They also did a massive firing when I left, anybody with a criminal record (felonly or misdemenor) was fired. About 150 people were terminated. Made the local news paper.
Overall, I couldn't see myself working at one for a career.