Webhook vs Polling for SMS Verification: Key Tradeoffs and Production Pitfalls

Phone number verification appears simple but becomes complex in production because SMS delivery is unpredictable and outside a backend's direct control. Developers typically need temporary rentable numbers and a reliable method to read incoming messages, either through polling or webhooks. Polling is straightforward but inefficient, making repeated API calls until a code arrives or a timeout is reached. Webhooks reduce request overhead to a single callback but introduce challenges like asynchronous context, duplicate events, and unauthenticated endpoint risks. A practical approach is to use webhooks in production with idempotent handlers and signature verification, while falling back to polling in test and CI environments.