Hey 👋
Honestly i don’t really use Wi-Fi Calling myself. However, last time i checked my carriers website (ID Mobile) they do infact support the feature on Phone 2 and 2a, so i imagine it would also work on the 3a series.
That being said, some carriers are either slow to update their list or just havent due to the fact that Nothing still isn’t as well establised as some of the competitors.
Simply put this is down to the carrier and you either need to buy a SIM and try it out, or contact each carrier to see if the feature is supported.
