In the US, ISPs are required to allow you to hook up your own modem. As long as your hardware is technically compatible with the network, you just give them you

In the US, ISPs are required to allow you to hook up your own modem. As long as your hardware is technically compatible with the network, you just give them your MAC address and plug it in. However, part of being compatible is that the modem bust be configurable and controllable by the ISP. The ISP will typically flash their own firmware to your modem without asking or telling you. The same applies to cell networks. The actual modem in your phone is running a binary blob provided by the network operator. This is done for very good reason, without control of all modems in the netork, the operator can't provide reliable service. A broken modem in the network screaming out non-compliant signals can screw things up for everyone. It's a necessary evil for the network operator to have privileged control over the hardware on their network. You solve this by treating your modem as a direct, untrusted, unprotected hole into the public internet. You also must assume that the ISP can inspect traffic on their network. To solve all of this, you put a firewall between it and your local network. I really don't think it's at all a problem for ISPs to have this level of control over customer modems. It is a problem when the ISP bundles the modem and router, but that's a different conversation. Just always use your own router.