Long story short: I found a technician who knows all the ins and outs of these older, analog phones, paid him $50, and over the phone he walked me through a "back door", into the phone's programming, and displayed that elusive security code.
A couple others had pinged me earlier, saying they had similar issues, so I thought I'd post this to the list.
It's great now having the phone activated, all integrated in with the MID, steering wheel controls, etc.
Let me know if you want more info on this guy. He said he'd be willing to help others, as well, and he had a few other tricks up his sleeve in case they had blocked the back door, etc.