It was definitely not a phish: it didn't try to get me to do anything, and the USPS tracking number was legit and originating from a legit Verizon Wireless warehouse. I did have a telephone interaction with Verizon Wireless yesterday (when the package originated), but wasn't expecting anything to arrive physically (I made a plan change,
which will turn out to be important). But the mail was odd: there was a mystery number in my address after my town name but before the comma, and the listed mobile number is our old _landline home phone number_ that we haven't used in four years.
So I started poking at my account to see what their understanding of what happened yesterday was, and I noticed that while the data plan I wanted changed was changed, it wasn't exactly what I had wanted it to be, and it showed as having a pending change. I went back to my notes, redid the steps that I had been directed to do (one of those reprovision account things), noted once again that no popup appeared, and, unsatisfied, called the tech support number I asked for at the time.
That was the only correct thing I did in this whole process. There's a sim card on the way (a duplicate of the one I already have, so, in true tech support fashion, "Just keep it for later"), and the mystery of the old phone number is that's what I told them my home phone number was and it just never got updated (boy have I run into that a lot over the years). I also figured out why the plan change I requested looked a little different from what I got, and have now recognized that before I go on the trip I did all this for, I need to call Verizon and make the rest of the plan change happen then.
I find it entertaining that the tech support guy is way better at ordinary customer service than ordinary customer service. I'm hoping he is paid in a manner commensurate with that.