Diverse electricity consumption and distributed production present serious challenges in future smart grids. Smart grid end users can have a role of a consumer and a producer at the same time. So-called prosumers are considered to play a major role in the future grid operation, management and maintenance. One of main concepts supporting this novel role is prosumer flexibility, namely an ability of the prosumers to adapt their consumption or production according to the smart grid needs. Understanding, managing and utilizing the prosumers flexibility remains a serious research challenge that needs to be evaluated and proved in practice. In this paper we will present a synergy of two research projects addressing the area of prosumer flexibility management. First one is a horizon project Flex4Grid, which aims at prosumer flexibility management by using advanced information technology solutions, while the second one is a national Critical Peak Tariff project in Slovenia, that enables distribution system operators to test novel prosumer flexibility management incentives in real life operation. The projects' cooperation allows to utilize modern smart grid infrastructure, boost its usage with advanced IT, and evaluate prosumer flexibility management in practice. We introduce the conceptual model and implementation of our technical solution, as well as some preliminary evaluation results of a large-scale pilot.