I have head of a custom SP they did for Spectras that involved a Real-Time clock of some sort that was implemented in place of the STATUS/MESSAGE and DEK features. The called it their ComEd mod, I believe. Somehow the STATUS or MESSAGE function would send a time-stamp or something like that, I never got a complete description of how it worked.
This does seem like it has an RTC in it, there is what looks like a cheap clock crystal and another precision crystal, or maybe that's a custom IC in the can of some sort - hard to tell from just one angle. Either way it has a very prototype-ish look to it, like there were not many made, perhaps.
Something else interesting is the long number on the bottom, that could be a unique ID or something like a silicon serial number, and that can may be an early Dallas 1-wire device or something similar.