Hi!
TLDR: My 1-yr old ZTE Z839 worked fine, but had a slow SnapDragon 210 processor. I moved the sim that came with the phone to a new unlocked Z986, which supports all the LTE bands of the Z839 and then-some, and I cannot get incoming calls, neither will the Z986 register with the LTE tower - with the SIM in it. But, it will register with the same tower, if I take the SIM out... however of course it says 'out of service'. I can only MAKE calls, and get 3.5G service on the Z986.
Everything I read seems to indicate the Verizon network does not have this model phone as a 'valid' phone in it's database, and so it's not allowing the phone to fully register on the network.
Visiting a Verizon store several days ago, while they were friendly, and polite, they were functionally useless. They couldn't get through to Verizon's overworked and understaffed (and probably underpaid) tech support department, and phone call from TS I was supposed to recieve (I have a backup ATT number too!) I never got.
Long version:
First the good part: I bought a $50 (new) ZTE Z839 (ZTE Blade Vantage) from Walmart, around Spring of 2018, a Verizon Pre-Paid phone. Coupling it later with a SanDisk 64GB U3/A2-speed MicroSD card (less than $20), and doing a factory-reset, along with installing IceBox as Device Manager/Owner {Go read numerous articles online on how to turn-on hidden 'Developer Options' and enable ADB, then read how to make IceBox the Device Manager/Owner}, which allowed me to freeze certain 'bloat' built-in apps, like Google Play Music, from ever running or updating,
.. And overriding the default manifest so apps would install to the MicroSD {'Force allow apps on external' is the name of the option, again, in Developer Options},
..And, press-and-hold the Settings wheel to turn on granual app notifications {Called 'System UI Tuner' - will appear on the Settings main list just below Developer Options},
..made the phone quite decent. I have many apps installed, and only about half the built-in storage used.
Because it had Android 7.x, the above features were built-in, as opposed to Android 6.x and earlier. I didn't need to root the phone to do all those things above, so OTA updates worked fine (system updates).
I wrote all that above, because people will be searching for information about the phone, and I wanted them to find out how it improved immensely.
The only problem with the above, is the processor is slow. A SnapDragon 32-bit 4-core 1GHZ 210-series processor, it will bog down when running Youtube playback in the background, and switching to different apps. It causes the stream to stutter, sometimes the application just quits.
Encrypted phone calls will drop, similarly, because the device does not have enough CPU power to do the real-time compression&decompression needed.
So, I recently tried to upgrade to a Verizon-branded, unlocked Moto G6, and Motorola (really Lenovo, a chinese company, that makes Motorola phones now, except for the first-responder rugged line), had disabled the device manager features, built-in to Android since v5.x, by having a hidden software app appoint itself device manager, directly after a factory-reset (before it could be set by the user), indicating they are trying to hide software from the user, and force the user to run every app that comes with the phone (and update it, taking up space), thus introducing security concerns, as the user loses control of the device they paid for!
They had disabled built-in accessibility features, also normally available in android, so I couldn't choose which buttons at the bottom did 'back' vs 'recent app list' (normally reversable on a stock Android phone).
Etc, so despite performing better purely speed-wise, it was a step backwards in usability, and I returned it within about a day (Amazon!). In it's place, I thought to go back to ZTE, as other than speed, the Z839 had performed so well.
I found the ZTE Blade Max 3 (Z986U) - new!, for less than the Moto G6 refurbished. It supports LTE Bands 2, 4, 5, 12, 13, 25, whereas the Z839 only supports 2, 4, 5, 13, and the Z839 is an LTE-only device. Additionally, the Z986 supports CDMA, GSM and UMTS. It's branded 'U.S. Cellular', and comes with a U.S. Cellular sim, but removing that and inserting the Verizon sim from the Z839, data etc, seemed to work.
Later, I realized when people called my Verizon number, they would get routed to voicemail immediately. Although I could place outgoing calls. Text messages, also worked only one-way: outbound. While the people at the Verizon store I visited, to fix the problem, were polite, they were of no help. Tech support was supposed to call me - I have a backup ATT number, naturally, because cell phone service terrible in the States - and these low-level consumer garbage phones are likely to break at any time. Nevertheless, I received no call, at my Verizon or ATT numbers, in several days hence.
Today, while swapping the sim, again, into the Z986, to see if I could gather any more information, I noticed the Z986 was running at 3.5G speeds, not connecting to the LTE tower. LTE Discovery, an app, shows, without a SIM, there is a 4-bar connection to LTE (but naturally 'out of service' without a SIM), and the same on the older Z839 phone (except, it works!). But when I put the SIM, from the Z839 into the Z986, and turn airplane mode on and off (resetting the connection), it only connects at 3.5G, and, again, won't accept incoming calls.
I need this fixed! Thanks.
