As mentioned, inbound is a lot better than outbound, but it also makes a big difference how good the company you are answering calls for is to their customers. I worked for a company that was pretty much bottom in its industry, so you would get people that had been in a queue for half an hour, and had big problems that no one had been sorting out for months, so they were obviously not very pleasant.
Its also not so bad if you’ve been trained to actually deal with the queries you are getting, but the call centres I’ve worked in have had very poor training programs, so people tend to find it very stressful for the first few months whilst they work out what they are doing. If you can sort peoples problems, then they usually stop shouting and swearing at you.
There is also the issue of pressure, in particular – call times. You tend to be given targets you have to meet for average call time, and average wrap up time (time spent writing notes at the end), and these are not always very realistic.