If you’re quick then you can get some good software for free, but first…
Hopefully you’re using Firefox already, so… go to the Firefox add-on’s page and look for Download Helper. When you go to YouTube, use Download Helper to download the .flv file.
Now, go to http://www.giveawayoftheday.com/ and get Moyea FLV to Video Converter for free (which at 4.25pm today means you have just over 15hours to still get it for free) and use it to convert the .flv file of choice to a .3gp which will play on your mobile phone.
Tada! Not bad for free!
TBD