Getting rid of my SIM card is attractive to me for financial and political reasons, but it would not be compatible with my loved ones' expectations that I be reachable in an emergency. Here's a compromise I have been thinking about; I wonder if anyone has experience making it work (or knows why it won't) on an unlocked iPhone 6:

    - Buy a pay-as-you-go SIM card with support for SMS and data, but no voice, for when I'm not on WIFI. 
    - When I am on WIFI, use VOIP for calling, and SMS and data as usual.

Possible challenges/questions I need to research more:

    - Will iPhone permit a SIM card without voice?
    - Can I receive SMS via WIFI when connected and via the burner SIM otherwise?
    - What service should I use for VOIP when connected, and for accepting voicemails when not connected?
    - I know Apple overlays its iMessages over SMS (which causes terrible headaches when someone switches from iPhone to Android, and no longer receives iMessages). How should I manage this?