OK guys, deep breath. This is a video of Portal being played on an iPhone, and it looks pretty good. But it's probably not an actual port of Portal.
The video says the demo was made using the Unity Engine, which means they took some Portal assets and made a small demo with them. They didn't take the full game and squish it onto the iPhone; what you see is probably the entire thing. There's no way the Source Engine is running on the 3G. Maybe the 3GS, but not the 3G.