[Galaxy S6 Active] A2K1:
Here is some important information for people who are thinking about getting this phone.

This phone is an astonishing piece of technology. Just a few years ago a water resistant smartphone would be two inch thick and weigh five pounds. Nevertheless, AT&T and Samsung only care about making money right now and how to invent new ways to abuse their customers.

First big problem: the phone comes packed with non-removable set of third-party applications and services many of which run in background all the time consuming battery and reducing operating system general performance. You can "disable" (basically hide the icon from launcher and prevent autorun) some of those apps using Application Manager, but most packages have "disable" button inactive and even more preinstalled packages do not even appear there. The ROM read-only settings do not allow to "disable" system services, only to "hide" them, you can hide services using adb shell or Debloater tool but that will not actually disable or remove them. Because of this the device has about the same battery life as regular S6 despite having a lot more capacity.

There was also an app which allowed to disable up to 10 background services and asked for money to disable more, but it was removed from Play Store by Samsung's request. So even if you somehow get the apk file and install it, you won't be able to block more than 10 services since only way to buy that feature was via Play Store. And I don't think that it really does anything on unrooted devices. I have seen processes running after disabling services they belong too with this app.

Second, bigger problem: AT&T has a way to force your phone to install software without your knowledge or approval. They basically have power to make any changes they want to the phone software. How is this even legal?! They have used this power once in last month to force people to install some suspicious update with no description provided (probably more third-party software). OK, maybe automatic updates are really not as bad as I put it, but just try to think about it like this: this phone has an exploitable backdoor which allows to alter phone software. Access to this backdoor is controlled by AT&T, and I am not sure what level of security they are providing, but if you try to google "AT&T security breach" you can see that they are having serious security problems pretty regularly, and we only know about really bad cases that were made public by press. So how long will it take for someone to find a way to use this forced update mechanism to remotely install malware on your phone? Hopefully not too long because that would be a great way to root the device and disable this AT&T backdoor service. They will definitely use this backdoor to block any root exploits that will appear soon. Please avoid using this phone for anything related to work or personal finance since any information you put into it will be under high risk.

Third, the root problem: yep, there is no root exploit available. Samsung made sure that when you google "s6 active root" you will get a bunch of tutorials how to root this device (it really helps with sales), but none of them actually work since phone was released with kernel version which had all currently known privilege escalation bugs fixed. So KingRoot, PingPong and all those firmware reinstallation methods using Odin simply won't work. Also their new "Pay" technology (wireless payment which uses magic to simulate card swipe, so it works with regular magnetic stripe card readers) supposedly checks phone for root and refuses to work on rooted phones. There is also a system service called "KNOX" which checks the phone software for modifications and will void the warranty and may brick the phone if it detects root. I would root the phone anyway, of course, it is completely worth the risk regarding the second problem.

There is some hope about this new MMS exploit that everyone are talking about past few days. It is hard to find any technical description, but it seems like a native media codec library has some vulnerability in it which allows to inject and execute machine code, so potentially it can be used to gain root access.

Not exactly a device problem, more like AT&T just being AT&T: they have blocked internet connection sharing over bluetooth, so you can share data connection with other devices using WiFi or USB, but not via bluetooth. That would be too convenient, right? It is not a limitation of my mobile plan, even my old iPhone (which is on same shared plan) allows me to share connection using bluetooth. It looks like AT&T have purposely disabled this function in G890A just to make fun of their customers.

And a small complain not related to the phone itself: Samsung's wireless charger is crap: you have to position the phone in a specific way to make it work, and even if it says it is charging it may stop randomly. This causes the phone to light up the screen in the middle of a night to notify you that it just started charging again after losing charger connection. Just get any Qi charger from Amazon/eBay instead, it will be cheaper and way easier to user.

TL;DR: DO NOT BUY THIS PHONE unless root is available. There is no root yet (July 29), and any website which offers root instructions for this phone is fooling you for ad profit. The phone is bloated with sponsored software which kills both battery and performance, AT&T has preinstalled a backdoor which allows them install any update or new software without your knowledge and despite your disagreement, bluetooth internet sharing is blocked by AT&T in a way that no third-party app can enable it, also rooting disables Samsung Pay and may void the warranty. I strongly suggest getting a Nexus instead of this phone, it is easily rootable and you could even get a water resistant case for it.