[OnePlus 6T  Questions & Answers] InvalidFelix:
Yes, This is true although what this does is take you off of FirstNet, it only gives you the same rate without being throttled, you will not get Priority over text/voice when using the AT&T Sim card.

As far as them stating that the FirstNet sim cards are not yet fully functional is false.

At the first of this year, I woke up to find out my service from FirstNet on my phone completely shut off, after talking with FirstNet they stated that my phone wasn't guaranteed full coverage as it's not a FirstNet compatible phone. Now it wouldn't be so strange that my phone got cut off if it had been any other day, but the 1st of the year, which is typically when new policies or procedures are put into place it happens that my phone got cut from having service?.. that's awfully strange, and now my phone that even though I stuck with it, having 4 months of issues with not being able to receive calls now it suddenly just doesn't do anything? When before I could call out, text, sms, use my hotspot and my data.

With this I felt betrayed and immediately switched to Verizon because here's the kicker. When I asked them the things I questioned about their "Compatibility" after doing troubleshooting, I asked the representative to explain to me what the issue was as I stated over the phone. "I don't understand why my phone isn't compatible, from my understanding it has an operating system that uses all of the features and capabilities that Oreo 8.1 has and more, including the IOC2/FirstPriority TM Software and Security update, It's able to use all of the bands required and everything sounds like it's more of a software issue but I don't understand why my phone, that was MOSTLY working before now suddenly doesn't work at all?" To which he had replied, not in exact words because I don't remember the exact words. "It's not approved by our network".

There it is, the biggest lie I've heard so far, it's not that our phones are incompatible, they're not APPROVED by FirstNet. But what is? Samsung, Moto, LG, Blackberry, iPhone. Your more expensive mainstream phones. In my experience this has lead me to believe they have a contract with these phone vendors and have a "VIP List" with them essentially, for what gain, I'm unsure of exactly but it's the only thing that makes sense. If this phone has all the features and security updates just like any other phone.. why is it unapproved?

I was able to trick their tower a couple of times to receive calls but I really feel like it's on their side and they're purposefully doing this to people who don't have phones that aren't on their VIP List, as a previous customer of FirstNet I'm disgusted with this fact as it makes me feel as though I've been falsely advertised to as "Compatible" and "Approved" are two very very different words meaning entirely different things, had I known that was the case, I might have gotten a different phone to save hassle, but, here I am..

Well.. That's my update.

I'm sorry to say this guys, the only way to have a One+ 6T phone on FirstNet is without being able to use the very benefits the network was created for and using it on AT&Ts network instead, for unexplained reasoning on FirstNet's part. The fact that they mixed those words just makes me feel as though it was intended to deceive the consumers and I feel very betrayed by the company and will not invest another penny into it, I feel as consumers we have the right to know what we're signing up for and we have the right to be informed and over all, we have the right to use the equipment we purchase.

Thank you for your time.

A Concerned FireFighter.