T1 Modem Variant Works in Librem 5

It’s still uncertain but the talk may have been at: Chosing the right modem PLS8 vs BM818 - #57 by amosbatto and follow the links.

Depends on which country - and whether the database (web site) is kept up to date.

Depends on which country - but if the data is there, I would expect it to be public i.e. where this is licensed spectrum, and a matter of public record.