There are 2 technical requirements you have to meet in order to watch videos on YouTube Mobile from your mobile device:
Your device has to support RTSP streaming. To determine if your mobile device supports this type of streaming, you may want to check your device's manual to find a description of its specifications.
Your service carrier has to allow streaming videos. You may want to contact your carrier for more information about the availability of data streaming on your mobile device.
Please note that YouTube Mobile may not exist in your preferred language. Stay tuned -- we're working hard to bring it to many other languages in the near future!