The iPhone Dev Team has been calling AnySIM open source from the start, even when it was called iUnlock. Friday they really made it open source, as they made the code available on the Google Code site.
The hope is that releasing the code as open source will decrease time between releases, as well as reducing the incidences of unstable unauthorized versions of the software.
The code is licensed under GNU General Public License v2. Since we're still waiting for an AnySIM version that will crack iPhone software 1.1.2, all I can say is: start downloading the code and start hacking, people!