Imagine my surprise when an eBay search for 'lineman' turned this up. I'd never seen one before, but knew instantly what it was.
Yes, it's the infamous blue box, as popularized by phreakers and yippies, and for a short time even manufactured and sold by Steve Wozniak. Its original owner, in a handwritten note, calls it a "black box" and mentions that she paid $200 for it in the mid-1970s. I have received and inspected it, and it appears to be in working condition (I'll test it later tonight), although with some cosmetic faults. It had a corroded pair of "Mallory Duracell" alkaline batteries which I'd date to approximately 1980 when Mallory eliminated mercury and manufactured only alkalines. Enough of that, here's some more shots.
The electronics (mainly two 555 timer ICs, the number pad, and a handful of discrete components) appear to be in working order, no burns or open solders.
For the uninitiated, Wikipedia (of course) has a great page about blue boxes. I haven't replaced the batteries and fired this one up, but I would imagine that the red button is the 2600Hz tone, while the toggle switch switches between 'normal' DTMF dialing tones, and a set of alternate tones whereby two of the keys (hopefully # and *) are mapped to 'ST' and 'KP'. One would 'seize a trunk' by blasting the 2600Hz tone, and place the call by dialing ST+10 digit number+KP, and thus call around the world for free. Bell System called it 'toll fraud'.
Whatever it was, it's history now.
-Chris