A commercially feasible plan for the development of ISAC networks is to leverage existing communication infrastructure, including the base stations, core networks, and edge or cloud computing devices. ISAC may also be outsourced to the massive user equipments (UEs), despite the challenges of mobility, low power, and low-cost hardware. On the one hand, existing hardware and signaling protocols can be leveraged for a fast deployment of ISAC networks. On the other hand, the intensive studies on 6G wireless networks will substantially improve the sensing capability of communication signals (such as mitigating autocorrelation sidelobes and shrinking the Cramér-Rao bound of positioning error).