During Market Garden. Then Lieutenant Ed Shames of the 101st Airborne (Band of Brothers) als led a recon mission to the Tilburg area (behind enemy lines). He could communicate with The US forces in Eindhoven via a Philips Company direct telephone line which was NEVER discovered by the Germans (until the end of the war). This line also came in handy for the resistence. Are there more examples of these undiscovered phone lines?
Source
Ian Gardner, Airborne the story of Ed Shames (I took an excellent Bastogne tour with him in 2008)
Background source, a local history page on this recon mission
https://www.oisterwijk-marketgarden.com/the_story_of_lieutenant_ed_shames.html