The cost and temporal characteristics of IT system’s Implementation, Maintenance, and Service jobs depend on the program code size and software complexity. The Process Approach can be applied to these phases of large-scale IT Project. Service Operations’ Supply Chain Optimization, in particular, can be effectively applied. The mathematical model is presented in this paper. It relies on the calculation of the parameters for multiple channel queuing model. This model is implemented in Microsoft Excel. It allows us to make estimates (in the Pre-Investment phase) for the average duration of maintenance and service jobs, and allows us to find the optimal team size for IT Service support.