The telephone number for Wolfgang Ritter that Gabriel dials has the wrong format and would not work (the "0" of the area code needs to be omitted when calling from outside Germany).
When Gabriel is talking with Wolfgang Ritter on the phone, Ritter refers to his home country as "West Germany". The game is set in 1993, three years after the German reunification. No German from that time (or even before the reunification) would refer to his country as West Germany.