I suggest you quit worrying about product knowledge and focus on BUSINESS requirements. My guess is that this project supports the customer relation department for a telecom company, so based on that I would look at what the business requirements for that. For example, simple self serve capability for customers (IVR aspect), ease of access between self serve and assisted service (CTI aspect), or back and forth between the two.
Key resources for getting the information include discussion with the business managers. Stay focused on business, and move away from too much discussion of solutions. Budget/cost issues are legitimate, and if there is a strong need to take advantage of or interact with legacy systems that are out of scope for the project, these too are business requirements. Make sure you get the experts on these systems identified so that technical requirements can be determined later.
Don’t forget the users – typically agents. They will have unique perspectives on what parts of their job are most important and what their tasks consist of. Again, its the business aspect rather than the technical aspect you are concerned with.
In short, your job is to clearly define the what (with priorities). Leave the how to the technologists.
Best of luck with your project!