To watch HD videos in YouTube in your iPhone 3g you must have Cydia and jailbroken iPhone with 3.0.1 IOS. Now Open your Cydia in your iPhone and add a new source to your Cydia. To add the new source click manage option in Cydia and then click sources, edit and then add. A box will pop up and you have to type http://repo.sinfuliPhone.com in that box. Now go to the section option and click sinful iPhone. You will have there all the available applications. Now search there for 3G Unrestrictor Cracked and install it. Now go to your new application Unrestrictor and click on edit and then + icon to add your YouTube application or whatever you want. Now you are ready to watch the HD videos in YouTube.