My experience is, where they're hiring, they're not laying off. I'm guessing that this CSS is some kind of Rep job? If being on the phones is your cup of tea, then good. They'll be metrics like talk time, your sales, etc that you have to meet.
Once you have your foot in the door, you'll have to work a certain amount of time before you can self-nominate for other positions in the company. My guess is, it's 18 months. To nominate for other jobs, you'll have to pass employment tests for the particular job title.
I got in years ago on a lousy job, (but not on the phones), passed a few tests, and got myself a high paying tech job. I am now retired with a pension and 401K, along with company health care.
It's not like you're enlisting. You can work for them, and if you don't like it, leave. I would give a 2 week notice and not burn any bridges, because maybe later on, a job that is a better fit could surface. AT&T jobs are located in a lot of states.