Looking at https://en.wikipedia.org/wiki/Telephone_exchange_names I see a few different mappings over time.

I like the fact that some of the earliest mappings had 0 mapped to "OPER" ("Operator"), because it makes me imagine that this number 33700 is like some interpretation of 337 and then shouting twice for the "operator" (as in, the literal physical person that used to sit and connect calls using wires and a patch board).

Taking this further then, and given that:

- 3 is assigned to any of the three letters DEF, and

- 7 is assigned to any of the three letters PRS,

we could invent the following meaning:

DES = "Déclaration d'Envoi de Spam". (Lit. "Declaration of sending of spam", as in a report about spam sending).

The double 0 is, as mentioned, in our invented meaning like shouting "Operator! Operator!"

And with this invented meaning it's like we are shouting for help from the operator to deal with this spam :D

Of course here I'm starting with 337 and backronyming "DES" to a plausible but probably weird sentence. If it was a real, the French would probably have worded the original sentence quite differently and the resulting number would be different as well.

(Also, looking at the article I'm not sure if any European countries also had 0 used for "OPER" or not. Guess I'll have to travel to some museums in France and have a look at some old phones with my own eyes at some point.)