Where is telephone country code 49 151?

00 isn't part of the country code, it is a commonly used international access prefix.

Country code +49 is Germany.

Area code +49 511 (or 0511 within Germany) is Hannover.

(The plus sign means "insert your international access prefix here." From a GSM mobile phone, you can enter the number in full international format, starting with the plus sign. The most common prefix is 00, but North America (USA, Canada, etc.) uses 011, and many other countries use different prefixes.)