The area code (phone code) 0511 is assigned to 4 locations in Germany. Mainly you reach landlines in Hannover (Niedersachsen).
|0511||Hemmingen / Hannover|
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 Hannover. So you can dial +49511... and add the number of the phone line you want to reach.