The Release of the Nintendo DS
The Nintendo DS released November 21st, of 2004.
2005
The first pass-through
The developer DarkFader gets his hands on the Nintendo DS, he wants to hack it. Others in the community started to capture to traffic of the cartridge (I assume Metroid Demo). DarkFader then saw header data, as well as encrypted data. He then figured that the RSA on the back, didn't apply to the actual cartridge.
He then made a programmable logic chip based pass-through that let him capture, and alter the traffic from the cartridge. DarkFader made an etched PCB that went into the DS, and a cut GBC connecter that held a DS cartridge. He then altered the header and figured out he could run his own code from the Game Boy Advance slot.
Once he could run his own code, he made a program that modified a string of text in the Metroid Demo, and then continued executing. That was the first pass-through.