In this paper we discuss the design methodology based on the service-oriented architecture and agile development principles for wireless embedded and sensor networks (WSNs). This methodology suits particularly well for streamlining and partially automating the design and implementation of complex WSNs. We report results from selected case-studies to test applicability of service-oriented architectures for embedded software. We evaluate the proposed design methodology by studying cases that include the development of three different services for wireless sensor networks that can work together as a part of a complete solution. We specifically comment on the trade-offs that a developer might face while designing and implementing systems. We follow the "best-practices" of the software design methodology and adapt them to the development of both the sensor network services and the sensor networks themselves. The design and implementation cycle includes three stages: the overall solution and architecture design, the protocol and application design, and finally, the implementation. These stages are iterated throughout the life-time of the project. During the design we consider both the abstract definition of user requirements and targeted functionality, and their mapping to the real hardware and software.