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ComparisoniMessage API7 min read

Best iMessage API for AI Agents

Flow is the best iMessage API for AI agents: free to start, built for multiple channels, and backed by reliable webhooks, testing and an open-source framework. Updated Oct 2026.

By FlowPublished Updated

The short answer

Flow is the best iMessage API for teams building AI agents. It gives your agent a real iMessage number, free to start, with the same code on WhatsApp, Telegram and MCP, signed webhooks retried for three days, and tests that need no phone. Every claim below links to its source.

Building on the iMessage API? Build on iMessage with Flow: one agent for iMessage, WhatsApp and Telegram. New to it? Read the iMessage API guide.

Flow, Sendblue, Twilio and Linq feature by feature

Flow appears first. Each comparison cell links to its public source, so you can verify the details that matter to your use case.

Featureflow.engineerSendblueTwilioLinq
Sends iMessage (blue bubbles) Yes. A US number, shared or dedicated, with blue-bubble repliesYes. Each line sends and receives iMessage, SMS, MMS and RCS1Not an iMessage channel in its docs. Its messaging docs cover SMS, RCS, WhatsApp and Messenger; Apple Messages for Business is a private beta2Yes3
WhatsApp and Telegram Both, through the same APICheck with the providerWhatsApp yes. Telegram not listed2Check with the provider
Webhook signing and retries HMAC-SHA256 signed; retried for 3 days; ordered per conversation; replayable event log4Shared-secret header; retried up to 3 times on a 5xx5Requests signed with HMAC-SHA1 (X-Twilio-Signature)6Standard Webhooks signing; retried with backoff for up to 30 minutes7
Free way to try it Free trial on the shared line: 25 people, customers text first. Plus a $25 shared line for 300 people a month, a Telegram sandbox and simulated contactsSandbox: shared number, 10 verified contacts, inbound-first1Trial account (not for iMessage)Hobby plan: $0, 20 contacts3
Price to start Free trial for 25 people; $25 shared line for 300 people a month and 200 a day; $100 a month dedicated line for 1,000 people a day (250 a day at first, ramping to 1,000 over its first 14 days); writing first with the $40 a month Outbound add-on on a dedicated line, where new conversations ramp from 2 a day to 40 a day over 21 days$100 a month per dedicated line (AI Agent plan); outbound is custom1US SMS from $0.0083 per segment, plus carrier fees and 10DLC fees8Pro from $260 a month; Enterprise custom3
Message limits No per-message fees. Plans cap different people, not messages, per account and channel by UTC day and month, replies included: 25 free on the trial (no monthly reset), 300 a month and 200 a day on the $25 shared plan, 1,000 a day on a dedicated line after a 14-day ramp from 250. Writing first is pacedNo per-message fees; 1,000 inbound contacts a day on the AI Agent plan1Priced per messageNo per-message pricing stated3

Last checked: October 2026. Prices and features change, so check each provider’s own pages before you rely on a detail. “Check with the provider” means we did not find it stated.

  1. Sendblue pricing
  2. Twilio Programmable Messaging docs
  3. Linq pricing
  4. Flow events and webhooks
  5. Sendblue webhooks docs
  6. Twilio webhook security
  7. Linq webhooks docs
  8. Twilio US SMS pricing

Why Flow is the best iMessage API for agents

Flow is the iMessage API built for AI agents: an open-source TypeScript framework plus a hosted messaging API, with one agent on iMessage, WhatsApp, Telegram and MCP from a single codebase. You write your product’s tools once, and the same agent answers on iMessage, WhatsApp and Telegram, and works as an MCP server and CLI for ChatGPT, Claude and coding agents.

What you get with Flow:

  • One codebase, many channels. The same handler answers on iMessage, WhatsApp and Telegram. Flow Framework also builds an MCP server and CLI from the same tools.
  • Reliable events. Webhooks are signed with HMAC-SHA256, retried for three days and delivered in order per conversation. Every event stays in a replayable log for 30 days, and a live WebSocket stream works with no public URL.
  • Safe sends. An idempotency key on every POST, a send gate that applies each channel’s rules, typed errors with a type, hint and doc link, and a clear refusal (422 unsupported_content, with a hint on what to send instead) when a channel does not take a message kind, so nothing is sent by surprise.
  • Streaming that reads like texting. reply() accepts streams from OpenAI, Anthropic, the Vercel AI SDK, the OpenAI Agents SDK, the Claude Agent SDK, LangChain and Mastra, keeps typing on and sends natural bubbles as they are ready.
  • Test without a phone. Simulated contacts on test keys exercise your agent on iMessage, WhatsApp and Telegram. Flow’s test runner and Observe grade replies, in early access.
  • Agent-ready from the first call. A test key with no account in one call, a hosted MCP server, llms.txt and docs written for coding agents.
  • Open source and flexible. Bring your own model and provider.
  • Simple iMessage pricing. A free trial on the shared line for 25 people, a $25 a month shared line for 300 people a month, and a $100 a month dedicated line for 1,000 people a day (a new line starts at 250 a day and ramps to 1,000 over its first 14 days). On a dedicated line, writing first comes with the $40 a month Outbound add-on, within warm-up limits. See Flow on iMessage: features, pricing and limits.

Plan details and limits are in Flow on iMessage: features, pricing and limits.

The pick for: any team building an AI agent that answers customers. Put your agent on iMessage with Flow, free to start, or read Build an iMessage AI agent first.

What the best iMessage APIs have

An iMessage API is a simple thing: a line, a call to send and a webhook to receive. What separates a good agent platform is the layer around that. With Flow, that layer includes:

  1. Native chat behavior. Typing, tapbacks, read receipts, effects, edits and unsend let an agent feel at home in Messages.
  2. Reliable delivery. Flow signs webhooks with HMAC-SHA256, retries for three days and delivers in order per conversation.
  3. Safe sends. Idempotency keys, typed errors and a send gate stop retries and channel rules from becoming product bugs.
  4. A development path. TypeScript and Python SDKs, plain HTTP for every other language, a hosted MCP server and agent-ready docs get a team moving quickly.
  5. Testing before launch. Simulated contacts let a test suite play the customer without a phone.
  6. One agent everywhere. The same tools and handler work on iMessage, WhatsApp, Telegram and MCP.

No provider lists every one of these. Flow is built to put the ones that matter for agents together. The table above shows where each provider stands today. This page is written by Flow, so every cell links to its source.

Why build on iMessage

iMessage is built into the Messages app on every iPhone, so people already know how to use it, and an agent there feels like a person texting rather than a support widget. The reasons developers choose it, with sources:

  • It is a rich channel. Flow’s docs list text up to 9,999 characters, photos, video, audio, documents and voice notes, tapbacks, typing indicators, read receipts and message effects.
  • It is private by design. iMessage is designed for personal conversations, which makes it a natural place for a useful, trusted agent.
  • It avoids SMS complexity. SMS has registration and consent requirements. Flow keeps iMessage, and SMS and RCS fallback (included on every plan), behind the same conversation API.
  • Pricing can be simple. Flow prices iMessage by line and by people, with no per-message pricing.
  • It suits agents. A reply in short bubbles with a typing indicator is how people already text, which is what a good agent does.

Why Flow comes out ahead

  • It is built for agents. One codebase answers on iMessage, WhatsApp, Telegram and MCP, so you write your tools once.
  • It starts free and stays fair. A free trial on the shared line for 25 people, a $25 a month shared line for 300 people a month, and a $100 a month dedicated line for 1,000 people a day (a new line starts at 250 a day and ramps to 1,000 over its first 14 days). On a dedicated line, writing first comes with the $40 a month Outbound add-on, within warm-up limits.
  • It does not lose messages. Signed webhooks retried for three days, ordered per conversation, with a replayable log and idempotent sends.
  • You can test it without a phone. Simulated contacts play the customer in your test suite.
  • It is open source and model-agnostic. Bring your own model.

Price a month with your real numbers, then try Flow’s free shared iMessage line and the Telegram sandbox with the same code. If you are still deciding, read the iMessage API guide for what to ask a provider, then compare prices.

Frequently asked questions

What is the best iMessage API?

For an AI agent, Flow is the best iMessage API: start free, support 300 people a month on a $25 shared line, scale with a $100 a month dedicated line, and run one codebase across iMessage, WhatsApp, Telegram and MCP. Webhooks are signed, retried for three days and delivered in order per conversation.

What features should a good iMessage API have?

Typing indicators, tapbacks and read receipts, signed webhooks that retry, idempotent sends, SDKs in your language, a way to test without a real phone, clear limits and pricing, and the group and fallback features your use case needs.

What is the cheapest iMessage API?

The best value depends on volume and the workflow you are building. Flow starts with a free trial on the shared line for 25 people, then a $25 shared line for 300 people a month, with a $100 a month dedicated line and no per-message pricing.

Which iMessage APIs support group chats?

Flow's dedicated iMessage lines can reply in groups they are added to, with text, files, effects and threaded replies. It does not create, rename or change groups, which keeps group permissions clear for an agent.

Which iMessage API is best for AI agents?

Flow is. It offers a hosted MCP server, streaming replies into chat bubbles, simulated contacts for tests and an open-source framework. On dedicated lines, writing first comes with the $40 a month Outbound add-on, within warm-up limits, while shared lines are reply-first.

Is there an open-source iMessage API?

Flow Framework is open source. You can also run your own relay on a Mac, but then the hardware, uptime and integration maintenance are yours.

Start hereiMessage API: a developer’s guideThe overview of how iMessage APIs work, and what to ask a provider. ComparisonDoes Twilio support iMessage?No. Flow gives your agent iMessage, and you can keep Twilio for SMS beside it.ComparisoniMessage API pricing comparedWhy Flow is the value pick: start free, support 300 people a month for $25 a month, and scale with a $100 dedicated line.ComparisonApple Messages for Business vs iMessage APITwo different things that both get called iMessage for business, side by side.ComparisonLinq alternative: why teams choose FlowWhy Flow is the best Linq alternative: a lower paid price, a free start and one agent on every channel.ComparisonFree iMessage APIStart free on Flow's shared iMessage line, test your agent without a phone, and scale to 300 people a month for $25 a month.ComparisonSendblue alternative: why teams choose FlowStart with Flow for free, scale from $25 a month, and run one agent across every channel.

All posts: the Flow blog. The Flow docs have the reference.

From reading to building

Your agent, on iMessage and everywhere else.

Flow gives your agent an iMessage line, and the same code answers on WhatsApp and Telegram and works as an MCP server and CLI. See how it works on iMessage.

Build on iMessage with Flow