There are ways now (as in, very recent) to bypass the ONT for AT&T, people have developed custom GPON SFP module firmware that lets you connect directly. There

There are ways now (as in, very recent) to bypass the ONT for AT&T, people have developed custom GPON SFP module firmware that lets you connect directly. There are also multiple ways to bypass the gateway authentication, be it extracting the certificates or doing Ethernet proxying of the authentication frames.