NSA phone hardening guide(imessage/facetime seems to be common attack vectors, so disabling those on iphones would be wise, but disabling those exculusive features sort of defeats the purpose of having an iphone.)
Sim swapping migration: Google Fi with Google’s advance security enabled. Mint might be an option as well (if they use TOTP etc.) and their support security.
Librem phones, GrapheneOS, Replicant
Phone/sms spam migration: enabling block calls not in recent call log/allowlisted in contacts. [Apple’s KB article on how to enable message unsolicted call feature] (https://support.apple.com/en-us/HT207099) [Apple’s KB article 2] (https://support.apple.com/guide/iphone/block-filter-and-report-messages-iph) https://www.fcc.gov/call-blocking https://www.donotcall.gov/ Might could register a phone number with Twilio to give out/sign up and then set up to forward to real number. https://www.twilio.com/labs/twimlets