While most RF-sensing approaches proposed in the literature rely on short-distance indoor point-to- point instrumentations, actual large-scale installation of RF sensing suggests the use of ubiquitously available cellular systems. In particular, the 5th generation of the wireless communication standard (5G) is envisioned as a universal communication means also for Internet of Things devices. In this paper, we investigate environmental perception capabilities in cellular systems, with a special focus on the upcoming 5G communications standard. In particular, we analyze the perception capabilities of existing cellular installations in the GSM band, which is expected to be used for 5G IoT. Our instrumentation exploits a passive system capitalizing on environmental RF-noise. In addition, utilizing a prototypical 5G system with 52 OFDM carriers over 12.48 MHz bandwidth at 3.45 GHz, we consider the impact of the number and choice of channels and compare the recognition performance with acceleration-based sensing. Our results in realistic settings with five subjects suggest that accurate recognition of activities and environmental situations can be a reliable implicit service of future 5G installations.