Prior to my real estate career, I spent many years as a management consultant. During that tenure, I saw a number fo call centers handling both inbound and outbound calls. Never did see an environment where the sales people were in phone closets.
I did see a lot of effort made in noise reduction. Higher walls between cubes and plenty of sound absoring material help to buffer otherwise wide open spaces. Using modular furniture also provided the most long term flexibility for future office arrangement.
I think with the right design, you can reap most of the benefit you are seeking without having to build a lot of walls and doors. Probably worth brainstorming the true business requirements (contain noise level, some amount of privacy, technology connections, room for laptop and papers, etc) and then seeking advice on how to best accomplish from a design firm.