It works! The NAGBox Lives!
Granted, it's only on a breadboard currently, so there's still some work needed to do to get it all consolidated onto a single PCB. But when I hit one of the physical buttons, I get a text message asking me to call...me (I can't very well be texting other people if this is going to be a surprise when they receive it).
I'm still waiting on a few parts I'll use in my final build, but I can start putting the PCB together at least. So, that's the next step.