No. You could get the SRT-6 either with or without. If your radio doesn't have a "NAV" button, you don't have it.

It was a $1,500 option - or something like that, but people sell them for far less nowadays. Check the for sales area, or e-bay.

One other thing I left out earlier. If you purchase and install a radio with a NAV, you'll need the NAV antenna as well.