The area code (phone code) 0621 is assigned to 3 locations in Germany. Mainly you reach landlines in Mannheim (Baden-Württemberg).
|0621||Ludwigshafen am Rhein|
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 Mannheim. So you can dial +49621... and add the number of the phone line you want to reach.