Replacing the standard 2-tap SMS opt-in flow with a one-time password (OTP) verification, the flow could improve user trust and perceived security. This could ultimately increase SMS opt-in rates while maintaining or slightly boosting email conversions.

An A/B test was conducted across several brands to compare the performance of a 2FA (OTP) SMS opt-in flow against the existing 2-tap method. Two versions were compared:

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Site visitors were randomly exposed to one of the two opt-in flows:

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• The control with a familiar 2-tap opt-in for SMS, or
• The variant that introduced a 2FA-style OTP input field.

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We measured:

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• Email Conversion Rate – % of visitors who submitted their email
• SMS Conversion Rate – % of visitors who completed the phone number OTP verification

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Conversion rates were calculated by dividing opt-ins by total popup impressions.

The OTP variant showed consistent SMS improvements across most brands, with email conversions remaining mostly neutral:

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The variant delivered strong SMS lifts across all tests, with one brand seeing a dramatic +47% jump. Email performance remained stable, with only one brand showing a slight dip.

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Switching to an OTP-based SMS opt-in flow led to significant increases in SMS conversion rates while keeping email performance steady. The added security step likely increased user confidence without adding excessive friction.The takeaway: when done right, authentication doesn’t just protect, it converts. For brands looking to drive SMS growth without compromising trust, 2FA with OTP is a high-potential play worth exploring further.