The project life cycle starts with the business plan, that is, what is your strategic plan to make/keep your company competitive. This plan dictates specific requirements that can be formulated into specific projects. All businesses have processes that they follow. These should be characterized, documented, and reviewed periodically for efficiency and usefulness. A change in the business plan, such as moving to a VoIP Phone platform could change the process in which calls are handled.
A change in moving to more efficient operations (again using the example of a VoIP phone system) would drive an overall Architecture to either fit into the existing system or move to a new platform. Specifics of what the new system is required to do will drive a specific design. Given a design, an assessment of vendors and available equipment would ensue.
The development of the system would be the next step either by custom hardware and software or Commercial Off-The-Shelf (COTS) products that require some configuration. The system would be unit tested, integrated with other parts and System Tested. Quite often an Alpha test of one system or user would be conducted. A second phase, or Beta test would be conducted with a group of users proving the system can be scaled for deployment.
Deployment and Training Documentation
These go hand-in-hand so as the system is deployed for many users, they are subsequently trained on the new platform. Deployment takes the best knowledge of the engineering of the system so that a 'cookie cutter' approach can be utilized to roll out a new platform.
Life Cycle Maintenance Documentation
This area consists of how one would normally operate a system and training new personnel, How to administer the system for changes, and scheduled maintenance of the system.
Realize that any engineering change at any point would necessitate looking all the way back to the beginning to make sure the change is relevant to the business plan and processes, desired architecture and design, as well as being supported by the selected equipment feature set and functionality.