# Oxtro blog

> Guides on phone verification, OTP, two-factor authentication and WhatsApp messaging.

Source: https://getoxtro.com/blog

- [The top 5 SMS verification providers, and when to send the code on WhatsApp instead](https://getoxtro.com/blog/top-5-sms-verification-providers-for-secure-user-authentication.md): Twilio Verify, Vonage Verify, Prelude, Plivo Verify and Sinch Verification compared by channels, fraud protection and fallback, plus when a WhatsApp code is the better choice.
- [How to choose an SMS service for two-factor authentication](https://getoxtro.com/blog/how-to-choose-the-best-sms-service-for-two-factor-authentication.md): A practical checklist for picking an SMS or OTP provider for 2FA, covering delivery in your countries, pricing model, SMS pumping protection, fallback, sender registration and autofill.
- [Verification APIs compared for developers](https://getoxtro.com/blog/compare-the-top-5-sms-verification-platforms-for-developers.md): How the major OTP and verification APIs work from a developer's side, from the start-and-check flow to fallback, idempotency, rate limits and testing, and how to keep your code provider independent.
- [SMS vs authenticator apps vs WhatsApp codes for two-factor authentication](https://getoxtro.com/blog/comparing-sms-vs-app-based-two-factor-authentication-services.md): The pros and cons of SMS two-factor authentication compared with authenticator apps, passkeys, email and WhatsApp codes, what NIST says about SMS, and which factors to offer your users.
- [OTP code not arriving? A troubleshooting guide for SMS and WhatsApp verification](https://getoxtro.com/blog/solve-sms-verification-issues-quick-troubleshooting-guide.md): Why verification codes fail to arrive or fail to verify, and how to fix it, from number formatting and carrier filtering to rate limits, autofill, WhatsApp delivery and SMS pumping.
- [Twilio vs Oxtro: which fits your WhatsApp messaging?](https://getoxtro.com/blog/which-cpaas-wins-twilio-vs-oxtro-for-your-business.md): An honest comparison of Twilio and Oxtro for WhatsApp messaging and OTP, covering the official API versus your own number, setup, templates, pricing model, team inbox, API and risk.
- [SMS vs WhatsApp for business messages: which should you use?](https://getoxtro.com/blog/sms-vs-whatsapp-which-platform-drives-better-engagement.md): When to message customers by SMS and when on WhatsApp, compared on reach by country, two-way conversation, media, delivery receipts, cost model, rules and risk, and how to use both.
- [WhatsApp automation on Android: tools, limits and strategies](https://getoxtro.com/blog/whatsapp-automation-on-android-tools-strategies.md): What you can automate in WhatsApp from an Android phone with the Business app, where auto-reply apps fall short, and how to move to a shared inbox and API without losing your number.
- [5 message patterns that get SMS and WhatsApp messages flagged as spam](https://getoxtro.com/blog/avoid-sms-spam-triggers-with-5-key-text-patterns-for-brands.md): The spam trigger words, promotional tone, caps and emojis, links and missing opt-outs that get business SMS filtered and WhatsApp numbers restricted, and the habits that keep messages delivered.
- [Build your own Android SMS gateway in 10 steps](https://getoxtro.com/blog/build-your-own-android-sms-gateway-in-10-easy-steps.md): How to turn an Android phone into an SMS gateway with a REST API, from choosing a SIM and open-source app to webhooks, delivery reports, Android's sending limit and keeping it running.