Vodafone and Telefonica O2 UK were seen as trailblazers when they announced a network sharing venture, Cornerstone (now called CTIL), back in 2012, when most operators remained sceptical of such moves. The two MNOs placed their towers into the joint venture to create a single passive infrastructure network, and followed with a programme called Project Beacon, in which they have shared some active equipment (base stations) and coordinated their programs to phase out legacy 2G and 3G systems and introduce 2G/3G/4G RANs. However, the demands of 5G are forcing a change of approach, and this may be a signal to other operators which are engaged in RAN sharing, or considering it (beyond passive masts, sharing remains quite rare). In parts…