Porting a Net10 (Tracfone) number to T-Mobile, if my Net10 phone’s underlying carrier already is T-Mobile?

I currently have a Net10 (same company as Tracfone) prepaid phone and am looking at T-Mobile‘s Even More Plus plan.

The problem is, the number port eligibility checker says my number already is a T-Mobile number. That makes sense because Net10 uses either T-Mobile or AT&T numbers in my area. A sales rep confirmed that this was the case, though in my experience sales reps don’t know much.

Can I buy a $20 prepaid phone from AT&T, port my current number to it, then port my then-AT&T number back to T-Mobile with a real plan? Has anyone ever done this?

Thanks.