What type of socket is this?

[CRZR25]

Hi,
I saw this type of socket here in the Netherlands for the first time, does anyone know what's this for?
Where I come from, this doesn't exist.
TIA

 

[snowhead]

Telephone socket;

Vintage Telephone Wall Socket Netherlands

Vintage telephone wall socket in the Netherlands

depositphotos.com

 

[telectrix]

Telephone socket;

Vintage Telephone Wall Socket Netherlands

Vintage telephone wall socket in the Netherlands

depositphotos.com

well found, that man. must get one of them for my mobile phone.