A:
NO this modem does not work with ATT... Only TW... Netgear has many types of modems, google and see which one will work with ATT.
Now as far as your speed goes...What are you using it for? How many sources are using your modem? First I would follow these steps. If your modem has a filter on the telephone wire,... REMOVE it, then check your internet speed. If it is still too slow or not working as it normally did contact ATT and they can trouble shoot your internet instantly. If it is a problem with your wires you need to call your phone company and they can check to see if there is trouble on the line. If there are no problems and you have the lowest speed, go up with ATT or check the competitive prices.
Again, this particular modem is only for use with Time Warner cable.
I hope this information has been helpful!