When exactly the porting of linux to the SIMpad started is hard to say, since the ports that are available build off of similar projects. There are a few similar devices on the market where linux already runs (e.g. iPAQ, Zaurus, Assabet etc.). So needless to say the first port was basically a "familiar linux", which was ported for the iPAQ, with a modified kernel.
The work on the SIMpad port was started by a couple of employees from Siemens in Switzerland, namely Juergen Messerer and Walter Schweizer. If you search the www.arm.linux.org.uk archives for "simpad" you will notice that Juergen did the hardcore kernel hacking that is still the building block for future development. After getting a kernel that boots on the SIMpad, most of the "familiar linux" binaries were taken as is (with the exception of xcalibrate) and put together to get a working linux environment. As you probably noticed the first port was based on "TinyX", a minimized XFree86 for low memory devices.
Since some users of "Familiar linux" also like a QT-based desktop, an alternative to TinyX was also developed - Opie. Opie is a fork off of the original QT-Embedded-based QPE (Qtopia Palmtop Environment) from Trolltech. Users of the KDE linux desktop environment will be familiar with QT. If you are interested in the details why and how the fork-off took place go to the Opie homepage and their partner sites. The original port of Opie to the SIMpad was done by Chris Martin and later optimised by integrating the SIMpad as a target for OpenEmbedded, the successor of OpenZaurus. Chris worked together with Michael Lauer of the OpenEmbedded core team to get this accomplished.
Both ports were originally based on a CRAMFS root filesystem which has it's advantages (good compression) and disadvantages (read-only). Needless to say, because of the "read-only" characteristic of CRAMFS it was necessary to start work on a JFFS2 root file system like most mobile devices running linux. The first JFFS2 images were released in the beginning of June 2003, approx. 3 months after starting this task!
Then the release of the Opensimpad Distribution discontinued and the SIMpad had only a little life by those who where familiar with OpenEmbedded. Then Fred and some others uploaded some images. Fred then put SIMpad into the Familiar distribution and he is now the SIMpad Kernel maintainer.