The area code (phone code) 04638 is assigned to 3 locations in Germany. Mainly you reach landlines in Tarp (Schleswig-Holstein).
Note for calls from abroad: In addition to the German country code (+49 or 0049) you can omit the foregoing zero of the dialling code for Tarp. So you can dial +494638... and add the number of the phone line you want to reach.