Adding SMS to existing email infrastructure can help increase user engagement by reaching users through their preferred channel. However, direct integration requires careful consideration of UX guidelines, templating, routing logic, verification, analytics, and failure behavior. It's essential to default to SMS for users who have opted in, use templates with dynamic personalization, and handle consent and preferences carefully. The process involves creating flexible templates, normalizing data, and building a fall-back plan for delivery failures. By following these strategies, companies can simplify their notification logic and improve user experience.