In Switzerland there are "old" and "new" telephone sockets. Marco's answer applies to the "new" one. If you have an "old" one, you need a cable like this::
EPV telephone cable 6P/4C T+T87 to RJ11
to connect your base station.

For Switzerland, you need an RJ11 telephone cable. Maybe you still have one from an old device. You can also order one from Galaxis: Wirewin telephone cable RJ11