Open Wireless Sensors are based on the Open Source Software and Open Source Hardware paradigms. The code used to program them and the information about the hardware design are freely released. We present the main characteristics of Open Wireless Sensor Networks (OWSNs) and report on two examples with the experimental results revealing the performance of OWSNs in terms of link quality and battery life. We demonstrate the relevance of using OWSNs in Next Generation Networks by showing the advantages of the Open Source model when applied to Wireless Sensor networks in terms of cost, personalisation and independence from a single entity as compared to proprietary solutions.