Things worth knowing
before you build.

Any Android phone with an active SIM and internet connection. Install the Relayion app, pair it in the Relayion Console, and get your API key. That's it.

Yes. Each plan supports a different number of paired devices. Free supports one, Starter supports up to three, and Pro supports up to ten. Each device is registered in the Relayion Console, paired with a physical Android phone, and assigned its own API key. Messages route to whichever device the API key is bound to, so you can spread load across multiple SIMs or dedicate different lines to different message types.

Yes. The app runs as a foreground service with a persistent connection to the Relayion backend. Mount the device on a charger in a fixed location: your office, server room, or wherever the phone lives. An unplugged phone that runs out of battery stops delivering messages.

The message is accepted and queued with status QUEUED. When the device reconnects, the API dispatches queued messages automatically, oldest first. No message is lost. You can track delivery status through the dashboard or by subscribing to outbound events via your webhook.

The app needs SMS access (to send and receive messages), phone state access (for multi-SIM targeting on dual-SIM devices), and notification permission (to run as a foreground service so Android doesn't kill it in the background). It does not read your contacts, access the camera, or transmit any data other than the messages you send through the API.

Yes. Every permission is scoped to what the app actually does: read and send SMS, identify SIM slots, and stay running. The app has no unrelated analytics, no access to your contacts or camera, and transmits nothing beyond the messages you send through the API. Device traffic uses a device token (not your API key) so your integration credentials stay server-side. If you have a specific security requirement or compliance need, reach us at hello@relayion.com.

No. Relayion charges a flat monthly rate per device. The SIM card sends the SMS and your carrier plan covers transmission the same way it always has. We charge for the relay, not for every message through it.

On paid plans, there is no monthly message cap and no per-message charge. Relayion uses your own Android device and SIM, so you pay your carrier as you normally would. What paid plans control is throughput. The plan tier determines how fast messages go out. On the Free plan, up to 500 outbound messages are allowed per month. If your use case fits within that, the Free plan works fine for any purpose.

Every device on your account has two throughput parameters. Burst capacity is the maximum number of messages the device can dispatch in a short window, which is useful for sending a batch quickly. Refill rate is how many new message slots become available per minute once the burst capacity is consumed, and it determines your sustained sending speed. Higher plan tiers provide a larger burst capacity and a faster refill rate.

Messages queue automatically and no error is returned to your system. The API accepts the request and delivers it as quickly as your plan's throughput allows. You can track message status in real time via the dashboard or webhooks. On the Free plan, once the 500-message monthly cap is reached the API returns an error and you must wait until the next calendar month or upgrade.

Yes. One device, up to 500 messages per month, no credit card required. The free plan does not expire. If your requirements grow beyond those limits, upgrading to a paid plan removes the monthly cap and gives you faster throughput.

When a reply arrives on the paired phone, Relayion fires an inbound event to your configured webhook URL within seconds. You can set one webhook URL per device or one global endpoint for all devices. By default the webhook payload does not include the message body. To receive the body directly in the webhook, enable the "Include message body in inbound payloads" option when setting up the webhook in the Relayion Console. If that option is off, your webhook receives only the message metadata and you can fetch the full message separately using the message ID from the payload.

Yes. When you create an API key in the Relayion Console, you bind it to a specific device, SIM slot, and phone number. Every request made with that key sends from that exact line. To send from a different SIM, create a separate key bound to it.

Any carrier whose SIM can send standard SMS. The phone's native system sends the message. Relayion routes the request to the right device and reports delivery status back to your webhook.

Messages originate from a real consumer SIM, so the process may differ from traditional A2P routes. That said, rules vary by country, carrier, and use case. Customers are responsible for ensuring their messaging complies with local regulations and carrier policies. If you are unsure, check with your carrier before sending at volume.

Relayion is intended for legitimate business messaging. Common use cases include appointment reminders, order updates, OTP delivery, staff alerts, and booking confirmations. Sending unsolicited, spam, or abusive messages through Relayion violates our Terms of Service and may result in immediate account suspension. If you are unsure whether your use case qualifies, reach us at hello@relayion.com before sending at volume.