these units are mini cell towers.
if you removed the unit and your VZW phones signal jumped up to full strength, and it go to poor strength when the unit is plugged up, seems you proven the point for the class.
usually you hear more people who use this unit will have the cell phones in the house on sprint (or VZW as they have one also) so one would not usually check if it impedes other carrier devices, but in your case it seems like it does some harm to your VZW signal...
if you removed the unit and your VZW phones signal jumped up to full strength, and it go to poor strength when the unit is plugged up, seems you proven the point for the class.

usually you hear more people who use this unit will have the cell phones in the house on sprint (or VZW as they have one also) so one would not usually check if it impedes other carrier devices, but in your case it seems like it does some harm to your VZW signal...