For sale is a Siecor Network Interface Unit, new in original packaging with Subscriber Installation Instruction 00-508-26, Issue 3, dated January 1987. The model number is not marked, and could be a 630 MM, 630 NI, 630 TD, 631 MM, 631 NI, or 631 TD. I believe this to be a 631 model as the cover does not show a jack and does not have lugs for hanging a wall phone.

Additional photos available upon request, though views may be limited with packaging intact. Please message with any questions. Thanks!