I have been there, Norman. I have myself worked in quite a few different call centres. Twice for major banks and once for a mobile phone company, as well as some smaller firms. All-in, I have about 6 years experience - what do you want to know? Feel free to PM me if there is any specific advice you think I might be able to offer.
For me, call centres were never really as bad as most people make out. Sure, the work is soul-destroying, but at the end of the day the jobs are simple. The customer service part of jobs is easy - you sit there and have a chat with someone for a few minutes at a time, and with your problem solving abilities it'll be a total breeze. Rule #1: be a nice guy.
The thing that got me with call centre work is similar to what would get me at the bottom line of any big organisation. From your supervisor up, everyone assumes you're incompetent. This is a bit of an old school attitude, and lots of firms are trying to modernize but it's still a huge problem. In some way it's good that everything is spelled out - but it's bad because it means you end up with only a few simple tasks to repeat to the ^10, and when things go wrong there's normally an assumption that you've somehow messed up. Otherwise, you'll find a totally different atmosphere with things like breaks. All of the call centres I've worked in have computer logging systems that record when you're no longer available for calls - the total of that time for the whole day should be 1hr. 30 minutes for lunch, and two 15 minute breaks. In the final call centre job I had if you went 1 minute (yes, 1) over this time you were docked 15 minutes pay - automatically. There's no ifs or buts, no explanations - it's automatic. This part of the culture is what makes the jobs difficult.
Having said that, for this sort of work the pay has always been reasonable to me and in sales there is *a lot* of money to be made considering the jobs are available without qualification. Once job I had when I was a student, for instance, I worked 16 hours per week, and would pull in £500 basic per month + £400 in bonus. This is somewhere between double and triple what my friends would make with similar hours. Shame that I am awful with money
I would try to get used to a particular way of thinking before you go into sales though. It sounds awful, but once you get a conscience you'll start to stammer - and if there's any hint of a falter, you won't get the sale. Pretend the customers aren't people. Yes, it's extremely important that you meet their needs - and only sell when there is a need for the product - but it's important that your mind is free of a worry that you're selling something that is somehow not fit-for-purpose. If they answer your questions, and fit-the-bill based on that, then you're done. Get the sale, and that's that.
You should also take care with the 'they call me' point - it isn't always what it seems. You might be asked, for instance, to talk to people that thought they were phoning up for something else. You might talk to people that specifically were phoning up for something else and have been passed off to you as an extra. Basically, don't expect that everyone that you speak to actually wants to talk to you.