My understanding is that wifi calling is not available for Tmobile's mvno's. You have to use t-mobile directly, either postpaid or prepaid.
dpham00, Android Central Moderator
Sent from my Verizon Samsung Galaxy Note 3
Originally Posted by Carol Eslinger
My settings are not mvno.
Dpham is correct. You're on a MVNO since you're on Straight Talk. This means you're using T-Mobile's network but from a 3rd party instead of directly from them. The wifi calling feature only works for people who setup their accounts directly with T-Mobile.