This Panasonic KX-T KSU telephone taken at my local Burlington Coat Factory. This is not to be confused with the DBS series that was on the market from the early 1990s to 2002. The KX-T systems replaced the DBS series (for reasons that isn’t well known), despite being the market for about the same time.
You wonder why there’s two handsets cables? I bet the sub/contractor didn’t have a replacement line cord and apparently terminated the cord with an RJ-11 plug, I suppose? Regardless, that other handset cable is serving as the line cable.