This telephone has a production code of BL7 = Berlin 1930, juli.
It is often called W28 or Modell 28, although Siemens & Halske called it the Modell 27.
There is nothing printed on the side, nor is there a small shield with the Rijkstelefoon logo like with the Heemaf built telephones.
I already had one of those, but this one is in far better condition and is in a more original state (dial, handset, line cord)!
Please note that this telephone also has a threaded hole in the base plate for mounting it on a stand, like on a Heemaf 1931.