New Greek telephone points are to the standard RJ11 - that is the same as the connector at the laptop end.
I presume that therefore such converters must be freely available in Greece, as they will have a similar problem internally.
Of course if your friend has a new telephone point, they'll only need a standard RJ11 to RJ11 cable that you can get anywhere - including, obviously in Greece too.
But maybe they have broadband? - which will be different again?