In my opinion having a common communication management plan for the company is a good choice until and unless some authority is given to make a few changes to the common communication plan depending on the needs of the project which may involve communicating with people outside the company involved with the project, contractors etc. Having a common communication plan will save time and the people working on projects will already be knowing how the communication plan works within the company for any given project except for a few changes, which will be made depending on each project. It may be seen that the major policies regarding the communication within a given company would remain the same for all projects and only a few things may be modified or some minor changes may be added.