Zeta SMS: Private SMS & API

Zeta SMS is the last SMS app you'll need on Android. It is a private, well-organised messaging app for you, and an SMS gateway with a secure API for your own software, on the same phone and the same SIM cards.

PRIVATE, EVEN OVER PLAIN SMS
• End-to-end encryption between Zeta SMS users, carried over ordinary SMS: no internet, no account, no server in the middle.
• You choose the key exchange: post-quantum (ML-KEM-768 combined with X25519) or standard elliptic-curve (X25519).
• Private messages never enter the phone's shared message store, so other apps cannot read them.
• Compare a safety code in person to prove that nobody sat in the middle. Groups can be private too.
• Block screenshots and screen recording of the whole app, like a banking app.

ORGANISED AND YOURS
• Pools: Family, Work, Friends… each with its own emoji and colour. Everything else stays in Default.
• Swipe right to archive, left to delete, or press and hold to act on several conversations at once.
• Your own bubble colours for every person, and a picture behind any conversation.
• Schedule a message for later. Block a number silently. Reply from the notification.
• Dual SIM done properly: each conversation remembers its SIM.

AN SMS API FOR YOUR SOFTWARE
Switch on the gateway and the same phone becomes an SMS gateway your systems drive:
• Send single or bulk messages, each with a priority, through a secure API: REST over HTTPS hosted by the phone (with its own certificate or one from Let's Encrypt), a WebSocket the phone keeps open from behind any NAT or mobile network, or simple polling.
• Every operation is documented on the phone itself, with an OpenAPI export for your developers.
• Queues, retries and a delivery report for every message, counted in segments, the way operators bill them.
• Each SIM learns its operator's real sending limit and keeps its own daily quota; routing can prefer a SIM on the recipient's network and refuse destinations outside your SIMs' countries.
• Received messages can be forwarded to your server or any web address, filtered and rewritten with rules: verification codes, alerts, orders.
• Several phones can work as one gateway, sharing the work and carrying on if one drops out.
• Test mode runs a request through the whole pipeline with the radio simulated, so you can build your integration before sending anything real.
• Or connect it to ZSMSG, the online control plane, to serve your own customers with API keys, usage metering and delivery reports.

The gateway is a subscription; the messaging app is free.

RESPECTFUL
No ads. No account. Your messages stay on your phone unless you forward them yourself. Contacts access is optional.

Encryption works between people who both use Zeta SMS; with everyone else, Zeta SMS is a complete, ordinary SMS and MMS app.

Recent changes:
• A licence key issued with your invoice can now be activated here, alongside the subscription.
• Losing Wi-Fi or mobile data is noticed within seconds, and the gateway reconnects on its own.
• Being connected and being able to send are now shown apart: a SIM out of service, or a phone in airplane mode, no longer looks healthy.
• Each SIM shows whether it can reach the network right now.
• A licence key covers every 1.1.x update.