Anytime you implement new technology, improve upon existing technology or simply intend to implement a project that impacts departments, or groups of people in any direct way you should at all times have a communication plan.
One of the biggest things I see often is a project reaching implementation (or sometimes at the end of implementation, if your lucky a bit before) not having a sufficient communication plan (or any at all in some cases).
What is a communication plan? To me it is the planned method as well as pattern to which you shall notify your target audience, as well as improve user response as well as acceptance. It has a target audience (or several) as well as the key messages or benefits that the target audience(s) are recieving from your new system.
It lets users know how they shall be effected, when as well as how they can receive training, when the new system shall impact them and/or be available, what tools they shall have available to them, related resources to decrease load on trainers as well as administrators while providing users with the tools to evangelise as well as get excited about it on their own.
Letting the effected users know how it shall effect their day to day employment opportunities or their business processes in a planned manner shall permit you to improve overall acceptance, understanding as well as decrease the resistance at all times encountered when a modification is implemented.
So next time you write a project plan, or are working in a project find out if there's a communication plan, as well as if not, find out why, because of the fact that odds are in an estimated every situation your project induces change, as well as without a plan on behalf of how to handle that modification as well as communicate it to the effected audience the modification won't be as well received.
Communicating my message to you,

Richard