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The only exception to that is if you purchase the iPad on contract with ATT Next its locked to ATT, It can be unlocked but you have to use a Sim card. ESIM is disabled on them.

That one's carrier "locked" to begin with anyway (more like carrier visibility/reveal rules). Apple Embedded SIM and eSIM work but can only be used with AT&T (should actually be setup with the iPad line when you receive it).

The Nano SIM slot is technically unlocked but if using another carrier, it has to be activated already before installing on the iPad as the same carrier visibility/reveal rules apply.
 
Are you still in the Sprint network? Or have you swapped out your SIM already to the T-Mobile version.
I haven't done the T-Mobile SIM swap yet, though it's my understanding that the iPhone 12 Pro Max that I have uses the T-mobile network as primary in the background anyway. I've read a bunch of horror stories about people that swapped out for the T-mobile SIM (service went to crap, no roaming, etc) so I'm holding out as long as possible.
 
The only exception to that is if you purchase the iPad on contract with ATT Next its locked to ATT, It can be unlocked but you have to use a Sim card. ESIM is disabled on them.
Understandable. Think when first electronic sims came out the carriers were locking them even though didn’t have contract. Think DOJ was actually looking into it but ultimately did nothing. Maybe worked itself out with new versions.
 
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