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SMS gives people a plain-text way to use your product. Flow can send through a Flow Messaging SMS sender or through your existing provider.

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Connect a sender

SMS is not a flow link --channel trial option. Set up your own SMS sender and credentials. With Flow Messaging, set FLOW_MESSAGING_KEY and FLOW_MESSAGING_SMS_SENDER. Add the channel explicitly: the starter’s fm.channels() does not automatically include SMS. In the starter’s src/main.ts, replace its channels assignment with:
src/main.ts — replace the channels assignment
The existing buildAgent({ channels, ... }) call and fm.start connection then include SMS. For production persistence and startup, follow Self-hosting. Check it worked: send a message to your own SMS number and verify the reply and tool event.

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Use your own provider

This configuration fragment adapts a provider client you supply:
Channel configuration fragment
Pass channel to your agent. Verify your provider’s incoming webhook, then call agent.message({ channel: "sms", from, message: text, messageId }) with its trusted fields. Preserve the idempotency key in your provider’s send operation when supported.

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What changes on SMS

SMS uses plain-text segments, without buttons, typing indicators or read receipts. Phone identities are normalized; configure defaultCountryCode if your provider sends national numbers. Flow’s channel rules handle STOP, START and HELP—keep consent and opt-outs consistent with your provider and sender configuration.