Questions about GPO Retro landline phone

Yes, it worked for me. Internet and landline together.

We're not sure, but we think not; the supplier doesn't mention it on its sheet. However, it does say: "COMPATIBILITY: Compatible with modern telephone banking switchboard, digital menus, etc, the vintage phone works with all analogue and digital home networks, such as BT and Virgin." You can find the manufacturer's manual here: https://www.gporetro.com/products/files/GPO_Pushbutton_EU_Manual_JAN_2018_v3.pdf

This is an analogue telephone and can be connected to an analogue slot on the router.