I have tested only WAG354G V1 AnnexA version, but they should all be the same.
Use it at your own risk, no warranties. Source code at http://dev.openwrt.org
Problems: power led is craaaasy.
Flash using tftp method: http://wiki.openwrt.org/OpenWrtDocs/Customizing/Firmware/PSPBoot
Modules for annexa/b, pppox & essential net packages by adding this line in /etc/ipkg.conf