In the 1990s, the two phone booths inside each trainset were connected to Deutsche Telekom's C-Netz by 13 so-called "Funkfeststationen". Inside the tunnels of the first two high-speed lines, repeaters were installed at a distance of 1500 meters that communicated with the trains using leaky feeders. Between the tunnels, directional antennas were used. Inside the trains, antennas were installed in the service cars. Calls cost 0.7 DM per time unit. The same time unit cost 0.23 DM when using a landline.