Yes, I've had this. It seems like it needs a little more than double the free space to install for some reason- either that, or iTunes reports the amount of free space inaccurately. Either way, I would suggest you delete one album at a time till you are able to install Navigon, then add them back to your phone when it's done installing. If you're at 3.3 GB now, you may only need to delete about another 200-250MB.