There's a very interesting article on the Worldwide Genealogy blog about Berlin directories.
I've failed to find people in the directory but now I realise I wasn't looking in the right place !
You need to read the whole article about Berlin directories but here's an excerpt:
"the Berlin directory sorts by surname and then occupation and then first name .... (mostly abbreviated),.... then by men, women ....
What's worse is that the directories like almost everything I've seen before World War II is printed in the Gothic German font making it difficult for foreigners to read and also a very small type face.