The use of existing measurements from wireless communication or navigation systems for opportunistic sensing of the environment is an emerging field of great potential. In the last two decades, the use of physical measurements from signals in GPS system, in cellular communication system and in communication satellites has shown the ability to monitor moisture, rain and other atmospheric phenomena. In each technology, the corresponding virtual sensor has to be characterized based on the physics which relates the available measurements to the phenomenon of interest. The major opportunity, however, is the availability of numerous numbers of such virtual sensors. In particular, when using near-ground wireless communication technologies, the number of such virtual sensors can be huge, and their use becomes a typical IoT application. Based on our experience and expertise with using measurements of the signal levels in backhaul communication microwave networks of cellular systems, in this paper we will focus on the IoT framing of this technology and will discuss specific challenges and opportunities.