The future delivery of intelligent services and the sustainable digitalization of industry can be enhanced through the ongoing integration of Internet of Things (IoT) smart sensors with the fifth-generation (5G) wireless ecosystems. 5G-IoT technologies are intended to support a variety of use cases, each with different requirements. These applications are so diverse and demanding that 5G networks must be adaptable to a wide variety of individual scenarios. One of the main use cases for 5G-IoT technologies is smart cities, which prioritize enhancing the quality of life, fostering teamwork, and resolving resource limitations. Typical smart city networks include a plethora of services related to smart buildings, smart offices, smart industry, smart universities, smart transportation, smart health, and more. This paper aims to explore role of 5G-IoT technologies for developing sustainable smart city systems, including the role of mobile operators to enable innovative smart city services