This Reddit thread concluded that because a T-mobile account was suspended for non-payment and the number is unportable while suspended that the customer was out of luck.
I don't see how that matters legally. The FCC requirement doesn't make portability conditional on some account status defined by the carrier. But IANAL.
Since T-Mobile holds the primary numbers for Google Fi accounts, going from T-Mobile to Fi legally isn't a port, just a change in T-Mobiles billing system.
I was just using T-Mobile as another example. OP wants to move from Google Fi to something else, and the reddit poster wanted to move from T-Mobile to something else. I wasn't suggesting a port from T-Mobile to Fi.
https://www.reddit.com/r/tmobile/comments/4wotw8/tmobile_won...
I don't see how that matters legally. The FCC requirement doesn't make portability conditional on some account status defined by the carrier. But IANAL.