Products

Flow FrameworkOpen-source, one codebase for every chat Unified APIiMessage, WhatsApp and Telegram Flow CloudHosting, tests and observability

Ships to

WhatsAppiMessageTelegramChatGPTClaudeMuseInstinctMCPCLI
PricingBlogDocs GitHub

ComparisoniMessage API4 min read

Sendblue alternative: why teams choose Flow

Looking for a Sendblue alternative? Flow gives your AI agent a free shared iMessage line, a $30 shared line for roughly 200 to 300 people, dedicated lines from $100 a month, and one codebase across every channel. See the comparison.

By FlowPublished Updated

The short answer

Flow gives your AI agent a production-ready iMessage number from free. Start with up to 25 people, support roughly 200 to 300 people on a $30 shared line, or scale with a dedicated line from $100 a month. One codebase powers iMessage, WhatsApp, Telegram and MCP, with reliable webhooks and SMS/RCS fallback built in.

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 and Sendblue side by side

Flow first. Every cell comes from the company's public pages, with the source linked.

Featureflow.engineerSendblue
Sends iMessage (blue bubbles) Yes. A US number, shared or dedicated, with blue-bubble repliesYes. Each line sends and receives iMessage, SMS, MMS and RCS1
WhatsApp and Telegram Both, through the same APICheck with the provider
Webhook signing and retries HMAC-SHA256 signed; retried for 3 days; ordered per conversation; replayable event log2Shared-secret header; retried up to 3 times on a 5xx3
Free way to try it Free shared line: up to 25 people a month, customers text first. Plus a $30 shared line for roughly 200–300 people, a Telegram sandbox and simulated contactsSandbox: shared number, 10 verified contacts, inbound-first1
Price to start Free shared line up to 25 people a month; $30 shared line for roughly 200–300 people; dedicated lines from $100 a month; writing first subject to availability and warm-up limits$100 a month per dedicated line (AI Agent plan); outbound is custom1
Message limits Replies within 24 hours are not limited. Writing first is paced, and plans cap people a month (25 free, roughly 200–300 on the $30 shared plan)No per-message fees; 1,000 inbound contacts a day on the AI Agent plan1

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. Flow events and webhooks
  3. Sendblue webhooks docs

Why Flow is the best Sendblue alternative

Flow is the iMessage line plus the agent platform around it: an open-source agent framework with a hosted messaging API.

  • You are building an AI agent and want the same code on iMessage, WhatsApp and Telegram, plus an MCP server and CLI from the same tools.
  • You want a simple start: a free shared line for 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 iMessage API pricing.
  • You want ordered, replayable delivery: signed webhooks retried for three days, delivered in order per conversation, with a replayable event log. See webhooks compared.
  • You want to test without a phone, with simulated contacts on test keys. See test an iMessage agent without a phone.
  • You want an open-source framework and to bring your own model.

For plan details, see Flow on iMessage: features, pricing and limits.

Worth weighing before you switch

Before you move from Sendblue, confirm the plan covers what you use today:

  • Groups. Do you create and manage groups, with names, photos and members? Compare what each plan allows.
  • Extras. Do you use App Cards or FaceTime calls? Check they are on the plan you would move to.
  • Price shape. Does a flat per-line price or a per-line price with a cap on people fit your volume?

Moving to Flow

Start with a test key through npx @flow-engineer/messaging init or the Telegram sandbox, then connect the same handler to Flow’s iMessage numbers. Flow uses one bearer key, HMAC-SHA256-signed webhooks and an idempotency key on every send, so your agent has a clear, dependable delivery model from its first test to production.

For the code, see iMessage API for Node.js and Python. For plans, see Flow on iMessage.

Frequently asked questions

What is the best alternative to Sendblue?

Flow, for any team building an AI agent. It runs one agent across iMessage, WhatsApp, Telegram and MCP, with a free shared iMessage line, 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.

Does Flow have everything Sendblue has?

For agent use cases, Flow gives you a US iMessage line with SMS and RCS fallback, typing, tapbacks and effects, and adds a hosted MCP server, simulated contacts for tests, an open-source agent framework and simple iMessage plans. If you use FaceTime calls, App Cards or group management, check those against Flow's plans first.

Can I use Flow and Sendblue together?

They solve overlapping problems, so most teams choose one platform. Flow gives you the messaging line, agent framework, testing and multi-channel runtime together.

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 200–300 people for $30 a month, and scale with dedicated lines from $100.ComparisonBest iMessage API for AI agentsWhy Flow is the best iMessage API for agents: one codebase, reliable webhooks, testing and every channel in one platform.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 200–300 people for $30 a month.

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