I didn't see this video, but this is exactly what I did today. Same cut exactly.
You need to finish the hack over Wifi, as the ethernet internet cable cannot fit into the iPhone, and you cannot install the SIM thing until the hack is done. The hack allows you to install third party apps, but it also bypasses Apple's AT&T activation, which is the key to the jail so to speak.
Thanks for the link though, it has inspired confidence in what I am doing. I let you know if it works, the SIM chip unlock that is. Here's
where I bought the chip. Scroll down for the video which pretty shows you everything.
The video doesn't include the first part though, you can read that on Life Hacker. Gizmodo's video is a little misleading, and the leave out small steps that makes it impossible to do what they are doing. Example: When at the start trying to get the iPhone to go into recovery mode, they failed let the viewer know the crucial part, as in the bit where you are not meant to slide the power off slider to turn the iPhone off, but you have to actually keep the sleep and home buttons pressed for about 20 seconds, even after the power off slider appears - you keep holding them. I got that bit of Life Hacker.