A tornado cut a path of destruction through the area served by the telephone system. It made many improvements to the canal, including the installation of a telephone system. This allowed blurring the distinction of key telephone system versus PBX telephone system. The incident also created a strain on Hawaii's telephone system. It is still on the manual telephone system. There are also services that will patch a radio signal to a telephone system. Additional handsets have a battery charger station that does not plug into the telephone system. The telephone system functions, albeit imperfectly. Telephone headsets connect to a fixed-line telephone system. Norway was the first country in to get an automatic mobile telephone system. Automation of the telephone system was started in 1920 and completed in 1985. These restrictions were mostly lifted following the privatisation and demonopolisation of the UK telephone system. The hardware technology was largely that of the commercial telephone system and oil exploration. The layers are symmetric, because in a telephone system callers can also be called. Delhi's first telephone system was established in 1911.