this passage coming from web and i found it when i was hunting for some converter  and i copied it here now. 
Convert YouTube to  iphone is easy with  Free YouTube Downloader and  Free FLV Converter.  The former is a free YouTube downloader for downloading YouTube videos and  flash videos from internet; and the latter is a free FLV to Video converter for  converting those downloaded flash videos and YouTube videos to other popular video  formats. 
    The tutorial below will show you exactly how to  convert YouTube to iphone video directly for playback on iPhone using the  above-mentioned free programs as a YouTube to iPhone converter. 
    Step 1: Launch Free YouTube Downloader and type YouTube URL in the  address bar. 
    Step 2: Click settings icon to select iPhone MP4 as the target output format  in "Auto Recording" tab in  the pop-up window. 
    Step 3: Select one YouTube video, click "Video" tab to watch it in the built-in FLV player and check  the YouTube downloading progress at the same time. 
        Step 4: When the YouTube downloading progress reaches 100% and a yellow  smiling face appears,  Free FLV Converter pops up automatically,  showing the ongoing youtube to iphone MP4 conversion progress.