This article takes a comprehensive look at the integration of mobile roaming, WiFi4EU and the smart city concept within the European Union in the context of sustainability. These initiatives form key elements of the digital development and transformation of European cities. Starting with a brief look at the functioning of the European Union’s internal market, the article briefly analyzes the objectives of these projects, highlighting their interplay and benefits for citizens. It focuses on the development of smart cities and the importance of digital connectivity in the process of building smart cities. It discusses the WiFi4EU initiative, which provides funding for free public WiFi networks and promotes digital inclusion. It also looks at the core pillars of smart cities, including digital connectivity, efficient transport, environmental protection, innovation and citizen participation. The article discusses the challenges associated with this integration, such as ensuring interoperability of different technological solutions and data privacy. It also highlights the importance of cooperation between city authorities, local communities and European institutions to achieve successful digital urban development. The research emphasizes the economic sustainability implications of these integrated technologies, considering the potential for innovation, job creation and economic growth within the digital and tech sectors. The main method used in the writing process was the analysis method, which was complemented by the comparison and synthesis methods. The final discussion assesses the benefits and challenges that this integration brings for the development of cities and the improvement of the quality of life of citizens. By critically examining the convergence of mobile roaming, WiFi4EU and smart cities in the European Union, this study aims to provide insights into the transformative potential of sustainable connectivity. The findings contribute to ongoing discussions on urban development strategies, emphasizing the need for a holistic approach that addresses both technological advancements and the imperative of sustainable practices for the benefit of current and future generations.