Hi @Veli-Jussi Raitila ,
Thanks for reaching out.
Is it possible to allow users to both sign-up and sign-in with a phone number only?
Yes, it is possible to do both signUp and signIn setup with Phone number for user flow or custom policy as passwordless option.
In SignUp/SignIn userflow, select the Phone SignUp local account under Identity Providers which will allow to SignUp using phone number after verification through SMS.
If yes, is it also still possible to provide a way to change the phone number? E.g. after a successful sign-in, prompt for the new number and change after the ownership has been verified (e.g. with an SMS).
Yes, it is possible to change the phone number after signUp using Change Phone Number if the recovery email has been setup on User flow.
Before SignUp the user, enable recovery email which is currently under preview in the SignUp/SignIn user flow which will help to the send verification code on recovery email while changing the phone number.
Hope this will help.
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