Best iMessage API for AI Agents

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.

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 capabilities call that says what a channel can show before you send.
• 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, Telegram and SMS. 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 shared line for up to 25 people a month, a $30 a month shared line for roughly 200 to 300 people, and dedicated lines from $100 a month. Dedicated lines can support writing first, subject to availability and 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, SMS and RCS fallback behind the same conversation API.
• Pricing can be simple. Flow prices iMessage by line and people a month, 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 shared line for up to 25 people a month, a $30 a month shared line for roughly 200 to 300 people, and dedicated lines from $100 a month. Dedicated lines can support writing first, subject to availability and 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

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