[AT&T Galaxy Note 3 Q&A, Help & Troubleshooting] BarryH_GEG:
The N3 will be my first "carrier" phone on AT&T in two years. I'm not thrilled and depending on what it's like using it I may sell it on eBay and get a HSPA Octa. Here's my thinking:

Pros

I've been fine with HSPA+ on my previous phones and use to pay $10 a month for unlimited data through the "non-smartphone" loophole that applied to phone's AT&T didn't recognize. That party's over. So now I'm paying for LTE and not able to use it. So with AT&T's N3 I'll finally get what I'm paying for and even get LTE-A when they start to roll it out; supposedly this year.

The international N3's are insanely expensive. Negri and NewEgg have the Octa's at $779 and up. On Next it's $35 a month, I have no contract commitment beyond the phone's payoff, and I can sell it on eBay if I want something new.

Service and repair. Whether through Asurion or SquareTrade getting a carrier phone repaired/replaced is easy compared to jumping through hoops to get an international version (non-warranted and non-supported by Samsung in the U.S.) repaired.

Cons

God knows what AT&T's done with the s/w. We know there will be tons of their specific bloatware. That doesn't concern me because it can be disabled and with 32GB of NAND the space it takes up isn't a big deal. My big concern is their modifying, neutering, or completely removing some of Samsung's stock apps and features. I can't root my phones because I connect to secure networks so I'm pretty much stuck with what comes out of the box. I'm scared at what's coming out of AT&T's box.

I loved being able to use any multi-CSC ROM on Samfirmware or Samsung-Updates to keep my unrooted phone always current. I've probably had a dozen updates on my N7100. Now I'll be dependent on AT&T. That alone could end up pushing me to an international Octa N3. Also, to support the new features of Knox, Samsung's seriously altered and locked down the bootloader. So who knows what impact that'll have even on international N3's when it comes to updates via Odin. I used to root my phone when I wanted to do someting to it (EG: Google Wallet) and then unroot afterward and run Triangle Away. That ship sailed mid-year and with the Knox enhancements isn't coming back.

AT&T's modified radio may be crappy and I travel a lot internationally. Also I'm guessing on Next the device can't be unlocked until it's paid off. The only reason this is acceptable in my case is I'm getting a 3G (Octa) Note 10.1 2014 which has a dialer and I can use it in situations I need to pop in another carrier's SIM and/or the AT&T radio isn't working well.

Dev support is going to be limited on the AT&T N3's compared to the international versions. It'll probably still be strong but not as simple, timely, and robust. It doesn't apply to my un-rooted situation but something for people to consider.

The moment I find a S-800 international device that's quad-band GSM/UMTS and supports AT&T's LTE bands I'll buy it and sell my AT&T version. So far the EU and Latin American versions of the N3 don't support AT&T's LTE bands. The UK N3's LTE bands haven't been announced yet but I don't have high hopes. There's a chance a Canadian carrier will leave their version of the N3 unmolested and with the same model number as the international version and that it would support AT&T's LTE bands. That would allow it to be flashed like a non-carrier Samsung phone via Odin (with the possible exception mentioned above) and still get LTE on AT&T. Same thing for Claro in Puerto Rico. I'm not sure about the flash part but even an unmolested Canadian or Pueto Rican N3 with AT&T's LTE bands might end up being better than whatever AT&T does to their version.

All just my opinion of course. ;)