In the 1980s, national telecommunication sectors in Western Europe were met with new political agendas of liberalization and privatization. Since then, telecommunication services have been turned over to private and multinational companies. As a consequence, the involvement of private actors is one of the main challenges as regards the security governance of ICT sectors today. In this paper, I approach this challenge from a historical point of view by studying the Danish telephone sector’s involvement in preparedness planning during the Cold War. In response to a 1959 law, the sector was itself responsible for planning for the maintenance of communications in case of a war. Accordingly, the regional Danish telephone companies participated in a wide range of security-related tasks. The paper demonstrates how this brought about a number of discrepancies between commercial interests and national security agendas, despite the fact that the Danish state had controlling interests in the companies. The participation of business sectors in preparedness planning is an unexplored topic in business history as well as in Cold War research, but the paper suggests that it offers valuable perspectives on the functioning of the Cold War security state and on public-private divisions of security responsibilities in general.