Traditional service composition approaches face the significant challenge of how to deal with massive individualized requirements. Such challenges include how to reach a tradeoff between one generalized solution and multiple customized ones and how to balance the costs and benefits of a composition solution(s). Service network is a feasible method to cope with these challenges by interconnecting distributed services to form a dynamic network that operates as a persistent infrastructure, and satisfies the massive individualized requirements of many customers. When a requirement arrives, the service network is dynamically customized and transformed into a specific composite solution. In such way, mass requirements are fulfilled cost-effectively. The conceptual architecture and the mechanisms of facilitating mass customization are presented in this paper, and a competency assessment framework is proposed to evaluate its mass customization and cost-effectiveness capacities.