This would be the case if your ADSL Modem had a built-in Wi-Fi router combo unit. Not all ADSL Modems are combos; I had one from Verizon (a Westell 6300) DSL Modem that had no Wi-Fi router function, so I had to buy a Cisco/Linksys Wi-Fi router separately as a 2nd device and connect that into the DSL Modem. Verizon then upgraded me to a newer version (Actiontec) which was a combo unit in 2014 due to problems with the old Westell units. I'm now on Charter (Spectrum) and they installed me a new ARRIS stand-alone Cable Modem-and I also replaced my old Cisco E2000 Wi-Fi router in February of this year to Cisco/Linksys EA6400.
If your AT&T router is a combo unit including Wi-Fi which it appears to be, then you should have them upgrade you. If AT&T no longer provides new combo units, and they install you a ADSL Modem only, you can then go to Best Buy or Staples or newegg.com online and buy whatever Wi-Fi router you want. I think neem will agree with me that you really need an 802.11AC type router (most modern) to give you the strongest Wi-Fi signal you can get, so at a distance of 75 feet from the router you should be seeing 4/5 bars on your signal strength icon; or 80%. If you scrimp on your router, and you only get 2/5 or 3/5 bars (40% or 60% signal) you can pretty much kiss goodbye any decent streaming of media from the Internet to your HDTV (such as Netflix we talked about).

I will only install the top name brands on this kind of equipment, Cisco/Linksys or Netgear. The other brands are junk IMO. This router was brand new last year and top-rate by PC Magazine and others as well:
Link Removed
I paid $300 for it for my customer who has a huge 3-story mansion with 6200 sq. ft. It works awesome for him; and he has like 25 devices on his home network including his custom home theater room. The price has dropped in half to $169.99 at amazon as in the link above. This is the best one I've seen yet for the price.
If your AT&T router is
NOT a combo unit, then you should be able to buy whatever Wi-Fi router you want from whatever seller or store you want as I indicated above. It is important to spend the money and get a high-quality name brand. If you don't you will be back here in 2 weeks complaining about your crappy Wi-Fi signal and how things are still lagging/buffering.

Just sayin'.
I haven't had any customers in over 5 years with AT&T since they are not a provider here where I live now *resort town*. I actually had AT&T about 10 years ago, and back then they were providing the combo units. The thing to remember with Combo units:
DO NOT BUY THESE FROM 3RD PARTY OR ONLINE AFTERMARKET PLACES SUCH AS EBAY!! It's better to buy or lease the combo unit directly from the provider, AT&T in this case,
and tell them you want one from a AT&T service truck or wherehouse!
This is because if you are leasing that equipment from AT&T on a monthly basis, it's called
"Premises Equipment", AT&T owns it and therefore makes sure, in fact must guarantee it if you read your Service Agreement with them, to operate correctly. This requires them to have the latest firmware and updates to operate correctly on their network. If they install or send you a combo unit that fails their loopback tests, then they have to pay to replace it with one that will. I've worked for 3 different phone companies, and this is a well-known fact.
Bottom-line, don't try to cut corners by buying a Combo unit from anyone else than your provider (AT&T)!!
So you know, Combo units go from $50 (Verizon) to $250 or so in the ADSL Modem configurations. Most providers will lease you a new unit for $15/mo. or sell you one for full-retail price. If you decide to buy it and save some finance charges, you can save $30-$40 or so, and even if you own the unit, your provider will still service it as if it belongs to them and not you--since it was an approved and tested model!!

If you are short on cash, I'd go with the lease option; I have done this with several providers in the past, Cox, AT&T, Dish, Road Runner, Charter, Verizon, etc. and it really works to your advantage. If you have to buy both an ADSL Modem and separate Wi-Fi router, that could cost you upwards of $400. If you can lease a combo unit from AT&T; you only have to come up with $15/mo. right now!!
If AT&T gives you a standalone ADSL Modem only, then you could buy a high-quality AC router such as this cool Netgear Nighthawk router! That's under $200 and should solve all your problems.
Put on your big-boy underwear and call AT&T and get a new modem or modem/router combo unit and get your Wi-Fi upgraded to a current technology and your problems will go away!
Let us know how it goes.
<<<BBJ>>>