Solved! SIM card is having an existential crisis - can't call up my provider because their call centers are in havoc. Anything I can do?

Kawaii Penguin

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May 21, 2015
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Hi, guys. I'm having trouble lately getting my new phone to work.
(note: this is a repost from tom'sHardware, I was informed kindly by a moderator that this site exists! hopefully I can get an answer here :)

Brand: ZTE Zmax Pro Z981
OS: Android 6.01 - Marshmallow
Carrier: MetroPCS

The gist:
The SIM card does not work. I've tried setting up the network by going into mobile network settings & manually choosing the network operator as MetroPCS (my current carrier), but it rejects the SIM card, giving the error: "Your SIM card doesn't allow a connection to this network."
I am currently unable to contact their call centers due to this pandemic going on - they closed down their centers entirely. I want to see if there's a way to fix this issue without having to file a request to them.

The details:
This is a weird situation, for sure. I'm not sure if this is an issue in the software or just the SIM card / provider.
I salvaged the board from my old phone (which has a badly damaged screen) and decided to stick it into a replacement phone (same brand & all). I wanted to use my old board because I had a lot of stuff in the storage and I liked the current settings I was using.. also, the new motherboard was extremely sluggish and seems to have had some damage to the GPU. This may have been my fault. I was taking every precautions necessary, though, so I feel like it could've been the manufacturer. I'm not too sure.
Anyways.
The installation of the old motherboard went okay, my main concern now relies with the actual SIM card. For some reason, it's not activating like it should.
I was able to get it to work on the new motherboard, but the new motherboard is extremely sluggish, as mentioned prior. The operating system was constantly crashing.

I want to know if a motherboard can store some form of unique identifier to determine whether or not the SIM card can function on it.
My previous motherboard that I'm currently trying to use on my replacement phone is being denied access to the SIM card. It's the exact same brand of phone and everything - so what gives?

Tonight, I'm going to attempt to activate it on the new motherboard, as the cellular connection had worked previously. Then I'm going to swap out the boards and hope the motherboard doesn't have some form of unique identifier.
I'll get back to this post if the above works or not, but please lend me suggestions if you have any in the mean time.


Update:
Currently on the new motherboard. Things are sluggish but, it's whatever.
I managed to automatically connect to a cellular network with the last mentioned method. It still did not give me a proper cellular connection, though.
I managed to get some statistics out through a diagnostics app. Even though my provider was MetroPCS, I'm somehow automatically routed to Verizon. The data connection is going in and out, mostly out. What in the world is going on? e_e
https://prnt.sc/roop63

Update 2:
With the new board, I was able to connect to MetroPCS's network and retain a 4G connection, long enough to be able to contact their 611 support number. The automated system told me the phone was not activated, and it seems their customer support closes at 11PM now and is not 24/7.
I'll make one more attempt to switch out the boards. I'll see if the cellular network can still connect then.

Update 3:
Switched back to the old (less broken) board, even did a factory reset. (prior to this all the sensitive data was backed up into my PC, so we're good on that front).
At this point, I just wanna be able to use my old motherboard, because it's actually functional and not constantly crashing. The SIM card does not like this board for whatever reason, I get the strange feeling that they have an identifier on the board and locked it out for some reason. Maybe because I got a replacement? I don't know...
 
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Solution
If the SIM card is not activated you will need to work with MetroPCS. When you change the system board on the phone the ID on the phone changes also so it will need to be activated again. It's the exact same thing as if you bought a new phone.
If the SIM card is not activated you will need to work with MetroPCS. When you change the system board on the phone the ID on the phone changes also so it will need to be activated again. It's the exact same thing as if you bought a new phone.
 
Solution