You have to be careful with that too. I had a tech come out to fix what ultimately ended up being a faulty ONT and doing the same thing, hooking his test modem up to the line to make sure it wasn't my router causing the packet loss. Next month my bill was double because Verizon claimed I had a second line attached, apparently the tech's router registered as a second device. Thankfully tech support was able to reverse that charge, but it was annoying.