Great, so now in addition to paying a monthly fee for internet service and a monthly fee for the modem rental, you also have to pay a monthly fee for your router?
I suspect many (most?) people may not know they can buy their own modem. Internet providers don't typically advertise that fact, since they'd much rather have the steady income from the modem rental.
You get an optical network terminal that converts the fiber to gigabit ethernet (the closest thing to a "modem"), but then you still have to use their router to plug into the ONT, because they use 802.1x auth on the network and the client certs are burned into the router.
You can't put their gateway into a proper bridge mode to use your own router. The best it allows you to do is "passthrough" where it puts a device behind the router in DMZ mode and assigns it the public IP address so it looks like bridged mode. The gateway still maintains its own internal NAT tracking table anyway.
At least they don't charge extra to rent the box.
There’s a hidden page to pass through. It works completely fine in my set up.
EDIT: https://www.att.com/Common/storefront/resources/pdf/att_brid...
A few years later, I was stuck with them again in another state and bought my own from their approved list...then a few months later that model was no longer approved and any issue was blamed on using an unapproved/outdated model.
Every month they would agree to waive the fee and promise to fix it, and every month it would be back on my bill.
This went on for about a year until I cancelled my service, and then they hounded me weekly to "return" the modem.