This phone was the French standard telephone until the U43 in 1943. Although 24 is a reference to the year 1924, it was not introduced until 1927.
This telephone was developed by the LMT (Le Materièl Télèphonique) company in Paris.
The dial is in a separate housing, because at the time large parts of the French telephone network were not automated yet. Because of that many dialles telephones were still in use. Many of these telephones were produced without a dial.
This telephone was designed to be retrofitted with a dial in the field, in anticipation of the progressing automation of the French telephone network.
This phone was almost always fitted with an extra receiver, also known as the mother in law receiver. This was because of the bad sound quality of the French rural lines. By using the extra receiver, the reception could be improved.
Although this phone does not have an internal ringer, it is an otherwise autonomously funcioning telephone.
Please note the handset, that was designed by Bell/Western Electric. This so called E4 model was introduced in France even before it was used in the USA itself.