A gateway is one thing and a modem is another. Can you clarify your post?
Here's a network gateway -> https://en.wikipedia.org/wiki/Gateway_(telecommunications)
No home internet from AT&T I've seen used that device.
If you can post the make and model of your Uverse modem then members can check into that.
Does anyone know of a separate Modem that will work with the AT&T Uverse System that will replace the supplied equipment, the NVG510 from Arris?