Communication should be present between all people in every branch of product development. Communication is the key for success in the development of a project and if even one part of a team is slacking in communication it can have detrimental effects on the overall project. It is the responsibility for the project managers to facilitate communication between all team members, but overall it is up to everyone themselves to maintain good communication between their peers. As far as the platform of communication goes I do not think it is an incredibly important decision. The only requirement is that it is accessible to all parties and a reliable means of communication.