This is not even an option in France (and some other country I think). The ISP provide you one "box" (a router) that do the whole Internet+Phone+TV package and

This is not even an option in France (and some other country I think). The ISP provide you one "box" (a router) that do the whole Internet+Phone+TV package and they refuse to support anything else. You can refuse to use their "box", but they won't change the price of the subscription, and they will not provide any help. And since they use some weird configuration and won't tell you anything about it, good luck being able to make your router work. One guy at work actually manage to use his own router with Orange, but it was a journey, and it break regularly because Orange can just decide to change one thing whenever they want. The only ISP that is not a full on professional ISP and let you use your own router that I know of is OVH, but they are very small compared to the very big consumer ISP.