The iPhone 3GS video camera does not have a zoom feature. The Video Zoom app adds the digital zoom capability to the 3GS video camera. It offers Upto 3x digital Zoom. You can also change the zoom level while recording but then the earlier selected zoom level would be over ridden. So if you change the zoom level from 2x to 3x on-the-fly while recording, the whole video will be post processed with respect to 3x zoom level. This means that the previous part of the same video which you wanted at 2x zoom will also be zoomed 3x. Therefore, it is not recommended that you change zoom level anytime after tapping record button.