The blog post above includes the fax numbers, suggests you send a message in Korean only with a photo of Kim Jong Il - because it is illegal to throw away images of the General Secretary. The message should not be confrontational, but be about sending factual information, making the recipient think, and it is important the faxes be individualised.
It IS an innovative approach. Takes a bit of effort to get some Korean written by those who do not know the language, and it isn't cheap. North Korea charges a lot of money to terminate any fax calls in its country (after all that's foreign currency it can earn from overseas telcos).
Imagine if you were in a totalitarian state, knew little better and received a fax from overseas that told you that some of the things your government told you were a lie. Would you tell anyone else? Would you keep it secretly? Would you send a response?