BYOP Device Selection

You must be.  

Compatible band info:   https://en.m.wikipedia.org/wiki/AT%26T_Mobility

3g 850 and 1900. Must have both.

LTE 2,4,5 12/17,30,66. (Either 12 or 17 and these are primary)

Best Buy has a huge selection of unlocked phones.  So does amazon.  Do not shop alibaba.

Im on my second  oneplus branded phone, my older son has last years Razer, prior to that had a Nexus.  Younger son still uses a Moto Pure.  I’ve also had a pixel, Honor 8.  Motorola makes several compatible and Nokia is back in the picture with the 6 and 7 for USA.

Some of those are also Verizon compatible also.

I was looking for a budget phone with 6gb of ram & 6" screen.  I saw tons of different ones from Huawei, BLU, Xiaomi, UMIDIGI etc.... All of which seem to be missing half of the LTE bands for At&t.  Unless im missing something there too?

Wait.... You had an Honor 8 that got LTE?  The one i really want is an Honor 8x but cant seem to find a variant that supports all the frequencies.  

The Honor 8 L04 was US compatible , sold at Best Buy and through Amazon.  I got mine free.  I won an Android authority drawing.  Came from New Egg with a second box of goodies.  

https://www.gsmarena.com/huawei_honor_8-8195.php#l04

The 8x does not have all the LTE bands for ATT, so no it’s not going to get LTE.

https://www.gsmarena.com/huawei_honor_8x-9313.php

How about the Huawei Mate 20 Lite?  That one has the right bands doesnt it? (The SNE-LX3 variant)

Now you’re  on to something.   It has band 17

https://www.gsmarena.com/huawei_mate_20_lite-9284.php

However still doesn’t say for North America, which would be warranted and made to compatible.  My concern is sometimes they still struggle to get LTE, even though they have all the bands.  

I encourage people to check out what Best Buy has available as they are all for the USA.  

 @adidaskid808 is into the Huawei phones and might have some suggestions. 

@eRok666
For all Huawei phones, you need to get the international version.
DO NOT get the one for Mainland China market.
From the Huawei website, Mate20 lite SNE-LX3 got the basic bands for LTE with AT&T.
But you should know better,Most USA Telco is not too user friendly with Huawei.
I had the Mate 10 pro,cannot get LTE with AT&T ,but T mob .Yes!
P 20 Pro,never test with AT&T.  LTE with T mob, in Canada LTEwith Rogers Wireless .
I still waiting for my Mate 20 X international version for Christmas 

Shnikes, I'm not giving up lol.  There has to be a US government friendly foreign manufacturer out there that makes big phones with big batteries loaded with lots of RAM isn't there?   I'll just throw it out there again just in case  anybody got any ideas.

@eRok666 
I had been playing around with all this under US$400 Mainland Chinese phones for a while.
Most phones I get are from sellers online.They all said it will work with AT&T / T mobile/ Rogers Wireless.....etc.
I'll tell you,some phones specs is not as they say. Some phones may only work in one half of a state,
the other half had no service. 
I still remember the Oppo phone a few years back I would like to buy from a friend.
3G got only 1900 .LTE bands only got 4/5/12 .We test the phone in Las Vegas stripe area using AT&T .
We stand outside the Treasure Island area.The phone only has one bar on the LTE.
We switch the phone to 2G/3G only. It got full bar,we try to make a phone call.press send,
No service!!! We restarted the phone,it drop down to 2 bars on 3G,try make calls again without luck.
we put the phone back to LTE,make calls again, it go though,but it cut off in 15 seconds, NO service again.

Would you like to buy a phone like this for only US$200 ????