This is partially incorrect.
If you cancel the line, or have the line suspended/ cancelled due to non payment, the credits will drop… however any credits you have already received will not be charged back.
Also, if one wishes to pay off the phone before the installment plan is done, they’re welcome to. This will allow them to unlock the phone. If they do it BEFORE promotional credits hit, the credits will not apply. If they do it AFTER credits start applying, credits will remain until:
A) promotion ends after 36 months
B) line is cancelled
C) a new installment plan is started on a line that has had the device paid off but the promotional credits are still being applied monthly.
The wording from AT&T says it can take a few months before the credits kick in.
To clarify, we would have to wait until the first credit hits before paying off the phone to unlock it - otherwise risk losing all the credits?