Did you know that you can do this too on the Samsung Galaxy S3?
It is slightly different to the One X in that you have to switch to camcorder mode and begin recording vide before the option is available. Whereas the One X has a camera and camcorder button on the same screen, but none the less you have the option.
Take a look at the screenshot on the right. You will see in the bottom right corner a camera icon. This is what you will see when you record video on the S3 and this is the button you press to take a picture.
It leave no shutter sound in the video recording, nor does it affect the video playback.
It is not a feature you need everyday, but it is quite handy!