they pay-off / trick a T-Mobile employee into re-assigning your Google Voice number to them. It's happened before with Google Fi, but I haven't seen any public information about this happening with Google Voice (yet)
Are you saying the Google Voice phone number lock is useless and that any carrier can just steal Google Voice numbers regardless of the lock status?
https://old.reddit.com/r/GoogleFi/comments/10pjtie/google_fi...
I don't work at Google and don't know if this is possible with Google Voice. However, Google Fi is their paid service, so I would assume that's the one they'd want to protect the most.
There arent any SIM cards to be hijacked with Voice because it don't provide cell service.