Hi Guys. Thanks so much for the info!
It seems the Honda dealership that originally sold my car didn't put the unlock code stickers anywhere, and the previous owner didn't include it with the owner's manual, either. After much checking, I found this out to be true.
Well, I ended up giving a call to my friendly neighborhood Honda dealership, and--over the phone--I got the unlock code after reading to them nothing more than the radio's serial number!
By the way, if you ever need a FREE unlock code during normal business hours and you really don't want to give any more info that what is necessary (or if you just stole a radio and need to unlock it), call Poway Honda in San Diego, California and ask for Stephanie in the Parts and Service department. Their number is (858) 486-4300 in the United States.
But again, thanks for everything!