Thanks for the reply.
So:
If I bought a PhatBox from PhatNoise in 1999, it would work if I bought their 1999 Phatbox and put it in a 1999 Toyota, right?
Yet, if I bought a 2005 Phabox for Vw/Audi it would not work with a 1999 Toyota radio?
No, that's not correct. You have to understand the evolution of the Phatbox (this is just off the top of my head, some specifics may be off):
1) Phatbox Red - basically a beta unit, supported Kenwood, firmware updates add support for most 1st gen headunits
2) Phatbox LE (silver) pre-2002 (approximate) - The first "real" retail model. Supports Kenwood, Sony, BMW, VW, Trafficpro, Audi.
3) Kenwood Keg - basically the LE in a new chassis. The 710 was the entry level, the 910 had an upgraded audio stage.
4) Phatbox Visteon - Only supported Visteon headunits. The only Phatbox to support Visteon headunits. Can't be used with anything else.
5) VW Phatbox - like the Keg, just supported the 1st gen headunits.
6) Phatbox LE (silver) post 2002 (approximate). Made hardware changes to support Toyota, Honda, Accura, Landrover, etc. Supports any Phatbox compatible headunit (except Visteon).
So it doesn't matter what year Toyota you have, the only possible match is the late model Phatbox. Period.
Also, to the best of anyone's knowledge, none of the OEM versions were ever updated with the new hardware changes - they were all based on the 1st gen Phatbox LE - so you are correct that it doesn't matter what year you get your VW phatbox, it's still not going to work with the Toyota.
Finally, none of this takes 3rd party protocol adapters into account. I'm just talking about native support.