Twilio integration for SMS, voice, WhatsApp and verification

Twilio suits products that need several channels from one provider:

• You need SMS, voice, WhatsApp and one-time passcodes from one account.
• You want to start in a sandbox or trial, then scale with Messaging Services as your volume grows.
• You want app-driven calls with your own webhook logic, such as notifications or an interactive voice menu.
• You want to check a phone number, such as its line type, before you send an SMS or a passcode. Lookup does that.

Plan around these before you commit:

• You text US recipients from standard long-code numbers. That requires A2P 10DLC brand and campaign registration, and unregistered traffic incurs extra carrier fees. Twilio's page gives no review time, so plan for it.
• You send in other countries. Sender registration rules differ by country, so check the target country first.
• You only send verification texts. For those, Twilio's page says Verify can be used instead of registering a campaign.
• You need Facebook Messenger in production. Twilio lists it as a public beta.

Twilio describes Programmable Messaging as one API for sending messages over SMS, MMS and WhatsApp. Programmable Voice makes and receives calls: Twilio calls your webhook and your server replies with instructions. The Verify API creates a verification service, sends a code over a chosen channel and checks it. Messaging Services group your sender numbers into a pool and add options such as sender selection and opt-out management. Lookup validates and formats numbers and can return line type and optional risk data. Helper libraries cover the main server languages, and mobile SDKs cover voice.

• Webhook signatures: every Twilio request carries a signature header. We validate it using the helper library, with all parameters, over HTTPS, and watch for the things that break the match, such as trimmed fields or a changed URL.
• Delivery states: a message moves through queued, sending, sent, delivered, undelivered and failed. "Sent" means the carrier accepted it, not that it reached the handset. Callbacks can gain new fields, so handlers must tolerate them, and logic should not depend on error message text.
• Opt-outs: Twilio handles STOP and similar keywords by default and blocks later sends, which then fail. We record the opt-out in your system and do not send a duplicate reply.
• Queueing and limits: Twilio queues messages and sends them within your rate limit. We design for retries and spread load across senders.
• Testing: test credentials allow only a few actions and do not send real messages or fire callbacks, and a trial account can message only verified numbers. We test the rest on a live account.
• Secrets: the auth token grants access and signs requests, so it lives in the environment, and Verify calls use an API key.

1. Check the rules for your countries: US registration and country-specific sender rules decide how long launch takes
2. Build with callbacks from the start: every message has a status your system records
3. Handle opt-outs and signatures: before any real customer is messaged
4. Hand over properly: the sender setup, credentials handling and callback logic documented, with notes on reading a failed message