If you send SMS one-time codes, there's a decent chance you're paying scammers to phone-spam themselves on your dime. It even has a name: SMS pumping . And it's not a rounding error — Elon Musk claimed Twitter was losing ~$60M/year to fake 2FA traffic before they killed SMS 2FA for free accounts. Here's how the scam works, why SMS 2FA is structurally expensive, and why flipping the direction — mobile-originated (MO) 2FA , taken to its logical end over iMessage — fixes both the cost and ...