[Jamaa]

Ok, did a reboot and the Wi-Fi trick didn't work.

What worked is:

Turned off Wi-Fi
Swiped down from the top of screen and turned off Cellular Data. Next I clicked on the 3 dots at the top right and clicked on Cellular Networks and then toggled OFF the automatic setting.

Turned it back on, and then turned everything back on again and boom. No more missing sim card message error cycle.

(I did all this earlier but I had assumed that turning off the Wi-Fi was the key step but it wasn't)

Conclusion, if you reboot your phone (while on T-Mobile network) expect to deal with this until they fix it.

[ElbertR]

My Key2 worked fine all day today until I got home and it started a continues cycle of disconnecting from Tmobile and reconnecting. Never connected for more than a few seconds.

I have a BBF100-2 (Black 64GB) PRD63825-004 on Software Version ACD175.
Been reading this thread and the claim that it is due to problems with the ACD175 software version.

Strange that my phone has been working fine for a long time. The update was done a while back. Didn't have an issue until today. No idea why it started acting up.
Tmobile support did not seem to have a clue. Tried resetting the network settings on the phone but that did not help. Numerous reboots did not help.
After playing with the settings I found out that changing the 'Preferred Network Type' in Network Settings to one without LTE will keep the phone locked on the TMobile signal (only without LTE). At least you can text and make calls.
There 5 options on the 'Preferred Network Type' drop down list. The first 2 have LTE. Using either one of those and the signal keeps on disconnecting/reconnecting. Only when I picked the 3rd one in the list '4G/3G/2G' did the phone stay locked to the Tmobile signal. Still wondering if it is really an issue with the software or if there is something wrong with the phone LTE hardware..

But for those who are also having this issue, try selecting a 'preferred network type' without LTE.

[ElbertR]

So a few hours later I left the house for a quick errand. Feeling adventures I set the 'Preferred Network Type' back to '4G LTE/4G/3G/2G (the first and standard option). It worked!, the signal stayed locked to Tmobile without switching off. So far it has been holding.
Not sure why it is working again. Not sure why it stopped working in the first place. Software glitch? Network configuration issue? Hardware issue? Who knows....

[Jamaa]

So a few hours later I left the house for a quick errand. Feeling adventures I set the 'Preferred Network Type' back to '4G LTE/4G/3G/2G (the first and standard option). It worked!, the signal stayed locked to Tmobile without switching off. So far it has been holding.
Not sure why it is working again. Not sure why it stopped working in the first place. Software glitch? Network configuration issue? Hardware issue? Who knows....

/blackberry-key2-f472/blackberry-key2-not-reading-simcard-1176935/#post13456181

[ElbertR]

I never got a message about the sim card. Just kept on dropping the Tmobile signal and reconnecting than dropping again after 2 seconds.

Still working like normal now. Problem so far has not returned.

https://forums.crackberry.com/showthread.php?p=13456181

[Jamaa]

I never got a message about the sim card. Just kept on dropping the Tmobile signal and reconnecting than dropping again after 2 seconds.

Still working like normal now. Problem so far has not returned.

Once you reboot the phone, the problem returns.

Also, the sim card symbol flashes on the top left of the screen. As "no sim card" and then showing a present sim card.

I'm thinking that after the reboot, the phone attempts to connect to the T-Mobile various signals, and it errors if one of the signals does not respond. Hence why I turned off the 2G thinking that perhaps T-Mobile has completely switched that signal off. And resulting in the no service error we're having.

Just guessing here.

[ElbertR]

Yes after a reboot the problem came back. Selected the first non LTE option in 'Preferred Network Type' and rebooted and the signal stayed locked again. Will give it a few hours and try the LTE option again.

[ElbertR]

The latest update ACE748 seems to have fixed this problem for me.

[Jamaa]

The latest update ACE748 seems to have fixed this problem for me.

Did you use the autoloader or OTA update?

[ElbertR]

Standard OTA update (Tmobile USA)

[Jamaa]

My PRD is 65000-XXX which probably means I'm a few thousand behind you if they're dropping this OTA based on sequence.

BBE100-5

[Jamaa]

Got the new update at almost 1am after checking for an update.

T-Mobile, Los Angeles

And it's fixed the no sim card issue