Smarter and greener cities are essential to address economic, social, and environmental challenges due to the increase in urbanization, requiring informed decisions based on Internet of Things generated data. A particular challenge is the unstable power supply of cities in underdeveloped countries (e.g. South Africa), thus requiring smart energy management. Future handling of grid overload in South Africa involves demand-response mechanisms, installing small devices at the end-user, communicating over different network technologies to a central controller, allowing loads to be measured and limited if necessary. Further challenges are the deployment of affordable smart sensors (e.g. ABS air sensors) as well as gathering information from nodes with limited power. In scenarios from energy consumption to waste bin levels, data is either sent over IP networks (which delivers data immediately) or collected in a delay tolerant mode by mobile devices of individuals or crowds. In delay tolerant mode the data is stored locally, to be delivered when a suitable network is reached. In cases of open data collection the devices in this Future Internet realm are targets of security attacks and might be vendor-locked with proprietary software stacks. Our approach to address these issues is to interweave a sophisticated Smart City Platform (CSIR) and an ETSI/oneM2M compliant Machine-to-Machine (M2M) communication framework (TUB/Fraunhofer OpenMTC) as well as a delay tolerant Smart Platform with the M2M framework. We emphasize secure identification and authentication of sensors and users as well as policy-based store and forward functionality. To validate our approach, we analyse the core developments in federated experimental facilities (testbeds) in Berlin (TUB) and Cape Town (UCT) using a Slice Federation Architecture (SFA) compliant testbed management framework (TUB FITeagle) and follow an empiric approach by conducting field studies (trials) in South Africa – Gauteng (CSIR/Eskom) and Spain (I2CAT/ABS).