I bought it on eBay. It’s an old black bakelite telephone from the 40s or the 50s. I’m not sure the exact vintage, but its old enough to have a dial instead of buttons, and there’s some letters on the bottom reading “C/D 12-55”.
It works fine, and its ring is much more pleasant than the modern telephone I replaced with it.
The best part is that it still has a label on the front of the dial giving (one of) its old numbers: UPton 0-4550. Ain’t that grand?