 The phone Peter Sellers uses in his bedroom is called a Ericofon,  made by L. M. Ericsson of Sweden. This is one of the very few  foreign phones allowed in the US at the time of filming by the then  telephone company, Bell Telephone, which held a monopoly on both  telephone service and telephone equipment in the US. Bell Telephone  felt so threatened by the unique European design (and possible mass  intrusion into "their" telephone network) that they designed the  "Trimline" phone as a countermeasure.