The cost of a telecom service development is correlated to the discontinuity and the complexity of the process. To solve this problem, we propose a method dedicated to telecom service development, called EA4UP method. The first EA4UP characteristic is the use of the Enterprise Architecture (EA) for the design activity. The EA promotes component reusing, and improves development process continuity thanks to a Model Driven Engineering approach. In this new method, EA enforces the transformation of an analysis model into a design model. The second EA4UP characteristic is to place functions in the core of the method (instead of data). The assessments of eleven projects allow to measure profits of this EA4UP method with regard to the previous ones.