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> I wish there was a way to reject all calls coming from numbers who aren't on my contact list.

What kind of phone do you have? There are definitely Android apps that do this. This is the one I happen to use, there are many others: https://play.google.com/store/apps/details?id=com.grus.callb...

I am using an iPhone. I wouldn't mind switching back to Android just for this feature.

This is already built into iOS, no 3rd-party software required (which would probably just siphon off your contacts).

Just go to: Settings > Phone > Silence Unknown Callers

(Calls from unknown numbers will be silenced, sent to voicemail, and displayed in the Recents list.

Incoming calls will continue to ring from people in your contacts, recent outgoing calls, and Siri Suggestions)