I used to work at a call centre. My stutter didn't come up in the interview anyway but at least in my country they would not be allowed to deny you based on that, most big companies use a score based system that removes a lot of bias. Call centre interviews are generally pretty standard, you want to think about how you have communicated in previous jobs/studies, how you work with others, examples of good customer service etc. Usually they are pretty desperate for staff as well so... It was actually helpful at the time in developing confidence to talk on the phone but it could be annoying stuttering saying 'hi' as the call started lol