When you hit the voice button push the help button on the screen beside the cancel button. This will list all of the voice commands by which screen you are in.
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04 T4R Sport 4x4 Jet black, 2006 Factory nav unit with blue tooth complete install.
There is a separate Quick Reference for the Nav you should have received with your truck. The voice commands are in the back of the quick reference as well as the help screen when accessing Voice Commands.