Comparing messaging APIs for AI agents: iMessage, RCS and SMS

Which channel should an AI agent use?

iMessage reaches iPhone users as a normal blue-bubble thread with typing indicators, reactions and read receipts. Apple publishes no API for person-to-person iMessage, so agents use a managed provider. Twilio's Apple channel, Apple Messages for Business, is a different product: a verified brand profile where the customer starts the chat.

RCS brings rich messages to Android and recent iPhones through carrier-registered senders. Twilio and Telnyx sell it directly. Managed iMessage APIs use it as a fallback.

SMS reaches every phone. From your own US number it needs A2P 10DLC registration, and on iPhones it shows as a green bubble.

Telegram and WhatsApp work when your users already live in those apps. In both, the user starts the conversation, and WhatsApp limits free-form replies to a 24-hour window.

Webhook or WebSocket: how replies reach the agent

A webhook needs a public HTTPS endpoint, signature checks, and a queue so the agent can pick the reply up later. That suits a backend that already runs on a server. Twilio signs with HMAC-SHA1, Telnyx with Ed25519, Blooio and WhatsApp with HMAC-SHA256.

An outbound WebSocket inverts the connection: the agent dials out, holds the socket open, and replies arrive on it. No public URL, no inbound firewall rule, no signature code. Claw Messenger works this way on self-serve plans, and the agent authenticates with its API key in the Authorization header. Photon offers a Socket.IO stream on its Beta product, and Telegram's getUpdates long poll gives a similar result.

Waiting for a reply inside one agent run

Agents often need to send a question and wait for the answer before they continue. With a webhook you build that wait yourself: store the inbound message keyed by phone number and resume the run when it lands. With Claw Messenger the wait is part of the tools. The MCP server exposes wait_for_reply, and the LangChain and CrewAI tools wait for one matching reply during the call. If the listener drops, replies saved while it was disconnected arrive when it reconnects.

Node.js: send and receive iMessage, and what it costs

With Claw Messenger, one WebSocket sends and receives. Leave service unset and each message goes as iMessage, RCS or SMS depending on the recipient. Each message event says which service carried it.

// npm install ws
import WebSocket from "ws";

const ws = new WebSocket("wss://claw-messenger.onrender.com/ws", {
  headers: { Authorization: `Bearer ${process.env.CLAW_API_KEY}` },
});

ws.on("open", () => {
  ws.send(JSON.stringify({
    type: "send",
    id: "hello-1",
    to: "+15551234567", // a number registered to your account
    parts: [{ type: "text", value: "Hi, this is your assistant." }],
  }));
});

ws.on("message", (raw) => {
  const event = JSON.parse(raw.toString());
  if (event.type === "send.result") console.log("send:", event.status);
  if (event.type === "message") console.log(event.from, "replied via", event.service, ":", event.text);
});

Full event shapes are in the API docs, and the quickstart walks through readiness, one send and the matching reply.

A worked example at 2,000 messages a month (1,000 sent, 1,000 received), with published US prices checked November 6, 2026:

The cheapest row depends on contacts, not only messages. Claw Messenger counts messages in both directions and caps registered numbers by plan (50 on Pro). A startup assistant with hundreds of users needs a per-line plan elsewhere or a scoped Enterprise plan from us. See plans and limits and what AI agent texting costs.

When another option fits better

• Twilio or Telnyx for high-volume SMS, international numbers, voice on the same number, toll-free or short codes, and a vendor your procurement team already approved.
• Blooio for the widest channel list in one API, a hosted MCP, and a documented hand-off from an existing Twilio number.
• Photon for one agent across iMessage, WhatsApp, Telegram, Slack and Discord, with a hosted MCP.
• Sendblue for an agent that users text first, with official Node.js and Python SDKs.
• Telegram for a free assistant only you use.
• WhatsApp Business when most users are outside the US and already on WhatsApp.

Questions

Sources

• Twilio: US SMS pricing, A2P 10DLC fees, webhook security, MCP server, Apple Messages for Business beta
• Telnyx: messaging pricing, number pricing, 10DLC fees, receiving messages, MCP
• Sendblue: pricing, webhooks, MCP
• Blooio: pricing, webhook signatures, MCP
• Photon: pricing, webhook signatures, MCP
• Telegram: Bot API, bots overview
• WhatsApp: pricing, messaging limits, webhook verification
• Claw Messenger: pricing, plans and limits, API docs, MCP server

Related comparisons

• iMessage APIs for Linux and cloud agents
• Claw Messenger vs Sendblue
• Claw Messenger vs Blooio
• Claw Messenger vs Photon
• Best iMessage API options compared by buyer
• How to add iMessage to a Twilio setup
• A phone number for your AI agent
• SMS API for two-way AI agent conversations

Claw Messenger publishes this page. We sell one of the products compared. Rival facts come from each provider's own site, checked November 6, 2026; where a provider does not publish a figure, the table says so. If something is out of date, tell us.