The Beta program is for unlocked phones only. Devices obtained through a carrier will have extra network provider software, so won't be eligible. Even if you can use other sim cards, it's still not totally unlocked.
The Beta program also has a quota of participants that will be required. Once full, the Beta program shuts to new participants
If you install this beta program and you don't know about software or about how to repair phones then stay away from this as you could end up with a phone isn't any good for weeks