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Is he on wifi where he is at, if so, i would turn on wifi calling till you figure out whats going on.

With the sim tool, just release the tray, no need to take it all the way out, as long as the no sim pops up.
Power off and on, when its back on push the tray back in.
What your looking for, when...

I don’t have a SE, i know the TFW 11 is provisioned on the sim card, and no type of toggling in the settings,

The 14 is...

Is this happening in his Home area, or somewhere else.

Voice & Data should be set to LTE.

What ever you tried with CS, did you remove and reinsert the sim card.

If there’s a setting, it would be under mobile data.

Try removing the sim card.