Conventional approaches to positioning using mobile devices focus on the use of global navigation satellite systems outdoors and the signal strength of Wi-Fi and Bluetooth indoors, which allows for an average accuracy of a few metres. With the availability of Ultra-Wideband (UWB) integrated circuits in upcoming devices, as well as the foreseeable additional implementation of Phase-Based Ranging (PBR) concepts, such as those expected within the context of Bluetooth channel sounding, opportunities are emerging to achieve decimetre-level positioning accuracy for everyone for the first time using a mobile phone. In this article, we describe and analyse such systems as a proof of concept. Our results from practical measurement campaigns in indoor and outdoor environments show, on the one hand, that both variants enable average accuracies well below one metre, with a strong preference for UWB. One drawback of UWB, however, is that, due to its low transmission power, it only works over short distances – up to around 20 metres in our measurements. On the other hand, the results demonstrate that a fusion of both variants is advantageous, achieving a further increase in accuracy of, for example, 10% indoors.