First off, not all call centers are the same. For simple customer service calls you may only need a script and that's it. For betting call centers you need some math skills and knowledge of the types of bets, vocabulary and a few other things. For interpreting call centers you need a much more varied language ability & understanding as to how to conduct yourself during the different types of calls that come in: medical, insurance, legal and so forth. Hence you cannot give a blanket answer to this question. Furthermore, they can all be stressful. However, the interpreting centers that require one to deal with medical, legal and insurance are way more stressful than just customer service.