There are no fewer than 12 telephones in Huis Sonneveld: two outside ones and 10 house phones. Since the two systems were separate, there are two phones beside each other in the parents' bedroom. In the 1930s, a telephone line was quite expensive: it cost nearly 100 guilders a year just for the line rental. But to the Sonnevelds, a telephone was an essential part of modern life so the house was connected from the very outset.