While I don't have Internet access via AT&T, I do have Internet access via an owned modem/router combo with Xfinity. In my experience, while I was also wary of potential bridge setting issues, the VELOP system *does not require* any external modem/router to be pre-configured for anything. Instead, the VELOP system attaches itself directly to an open Ethernet port on your modem/router and self-configures. In other words, once everything is set up, you actually have at least two SSIDs in action; one for your previous wifi network, and one for the VELOP mesh network.