At Send A Message you pay Palestinians 30 Euros, you can have your message of love or debt collection spray painted on this 620 Kilometer fence.  In return, you get 3 digital photos to share with those who the message is aimed at.

"a collaboration between Dutch advertising professionals and creative Palestinian youth, each message posted reminds Palestinians trapped inside the Wall they have not been forgotten, helping to keep hope alive. The project also allows those inside those wall to send one single, simple message: “we are human beings, just like you, with sense of humor and lust for life.” That’s why they do this, and enjoy it.

Part of your 30 euros money stays in Holland, to cover the (minimal) costs of setting up and running ‘Sendamessage’. The bulk of the money will go to the Palestinian NGO’s (independent foundations) doing the work. They will fund small social, cultural and educational projects with the money earned (from buying bicycles to fixing the roof)"

Why is the wall there?

The barrier is a highly controversial project. Supporters argue that the barrier is a necessary tool protecting Israeli civilians from Palestinian terrorism, including suicide bombing attacks, that increased significantly during the al-Aqsa Intifada; it has helped to significantly reduce incidents of terrorism from 2002 to 2005; its supporters assert that the onus is on the Palestinian Authority to fight terrorism.

Opponents argue that the barrier is an illegal attempt to annex Palestinian land under the guise of security, violates international law,has the intent or effect to pre-empt final status negotiations, and severely restricts Palestinians who live nearby, particularly their ability to travel freely within the West Bank and to access work in Israel.  In a 2004 decision, the International Court of Justice declared construction of the wall "contrary to international law."

Source: Wikipedia article 

No matter your view on graffiti or the Israeli/Palestinian conflict I think that this projects has some interesting implications and is worth thinking about how  terrorism, democracy and the role that technology will play in influencing them both.