First, in order not to duplicate this wish, this post is intended for both platforms iOS & Android.
We know that SMS Retriever exists, but in relies on a server sending the SMS (And the included costs), which for a few SMS has no implication, but when the Auth's are over 3K a month, the rates start increasing.
One wish would be to have the PhoneAuthProvider.verifyPhoneNumber feature from Firebase Auth into iOS and Android. Back in time I used the same client device to send the SMS, but nowadays there are policies which are very difficult for us to overcome against Google Play.
This Auth is documented at:
Android:
https://firebase.google.com/docs/auth/android/phone-auth
iOS:
https://firebase.google.com/docs/auth/ios/phone-auth
I think this library would help a lot for programmers which works with both platforms for the client.
Thanks in advance
FBP
PD: Please do not post libraries that cant be used on both platforms or involve an external server sending the SMS