[ZenFone 2 Q&A, Help & Troubleshooting] kadmobile:
I flashed newest ASUS fw, it worked. My thoughts...

Ok, I had to pick up a Go phone as my HTC M7 finally bit the dust a couple days into this trip. There is one AT&T store on the island, so I gave the ZF2 a try. The ATT stock firmware felt laggy, obnoxious. Turned off animations, killed apps, was still disappointed. I didn't realize this was an Intel processor phone when I picked it up, so I realized that tons of ARM stuff will run emulated, making everything molasses. The phone is extremely RAM limited, so the ATT bloat background apps was the last straw... figured I'd take the plunge, here are my notes...

The post from AlexBodewig is accurate, I successfully updated phone with the "World Edition" firmware that was just released, UL-ASUS_Z00D-WW-12.16.5.112-user.zip following those directions. Also thanks to shawnchalfant at this thread where I first read this was possible: http://xdaforums.com/zenfone2/general/att-zenfone-2e-helpful-enjoy-t3233093 ... Also the OneClick root and CWM root thread, http://xdaforums.com/zenfone2/general/root-newbie-root-instructions-zenfone-2-t3114063

FWIW, I skipped pre "wiping" as I had only used phone for a couple days. All previous user settings worked successfully to the new image. However, I did not know you were not supposed to delete the bloatware apps! According to a couple threads, sorry, lost the links, deleting will cause you to bootloop the phone if you upgrade the firmware again!!! BEWARE, and try and use CWM to make a full backup to an external SD Card.... Also, I had upgraded SuperSU, and a also saw a ZF2 thread warning against doing that. So those are follow-ups for those of you looking to update firmware.

I think this information (http://xdaforums.com/zenfone2/help/att-lte-4g-issues-zenfone-2-north-t3126625) about LTE and this phone may be somewhat incorrect. Another thread prompted me to call ATT to see if I needed my SIM swapped, thinking LTE was deactivated on the IMEI now (http://xdaforums.com/zenfone2/general/4g-lte-confirmed-att-t3073711/page2). Bottom line, you can get LTE after the flash, but it is not the same modem baseband, so beware. ATT cannot access the phone's firmware (according to tech), and maybe that's a plus, but I think the WW baseband firmware

In fact, backup what you have in /asusfw/modem/ first, or wherever you see the .fls file. After upgrade, it was: /asusfw/modem/XMM_7160_REV35_1538.00_V1.3_signed_MIPI_FLASHLESS.fls You may be able to reload your original ATT baseband in ADB, or inject it back into the update.zip before CWM flash, or take the WW baseband out before flashing?

Before the ASUS firmware, the ATT image did show an "LTE" logo along with "4G" on the phone. The ASUS image will not show "LTE", only "4G". What concerned me more than anything about this upgrade was immediately before the flash, the phone showed a 2-3 bar LTE signal, and after update would only connect to HSPA/HSPA+ in the area I'm staying.

With the stock Zen Max2 I am getting 2-3 LTE bars back where I started before the flash. So the ASUS firmware has some issue either with the WW baseband, and the tech support rep though it was odd I did not have a data enable/disable mode where it was on stock firmware. In hindsight, maybe I had left Wifi on, so 4G was hidden when I was at condo. I just recall being stuck on HSPA, though on way to store, I could get LTE.

The ATT rep was fine with it being firmware from ASUS website, and not Cyanogen or something, so I just returned it for the Arm ZTE phone. I liked the build quality of the ZF2 phone, and camera, but the weak x86 processor was a deal breaker for me.

Hope this helps someone!