The test surface
The public sandbox lists 50 messages daily, API and SDK access, webhooks, typing indicators, receipts and reactions. That is a useful scope for planning a two-way prototype. Verify any recipient or account restrictions during signup rather than treating the daily message allowance as the whole sandbox contract.
The line plan
The production Line plan is $99 per month for a dedicated phone number and managed infrastructure. Enterprise is quoted for volume, custom integrations and SLAs. Unlimited messaging on the plan page does not establish unlimited newly contacted users or unlimited request throughput.
The proof to request
messages.dev markets iMessage, RCS and SMS through REST and a TypeScript SDK. Inspect webhook signature instructions and event identifiers before connecting a model. Then exercise a duplicate event in your own application and confirm only one response is sent. Our review identifies a product worth evaluating; it does not supply measured reliability results.