The problem
Sending SMS to US numbers at scale means 10DLC: brand vetting, campaign approval, weeks of paperwork — and aggregator pricing on top, around $0.0075 per message and up. For smaller players working in GoHighLevel, lead-gen operations, and fleets that don't have specialized SMS needs, 10DLC doesn't do the job — it's expensive, slow, and creates painful paperwork that pushes them toward notifying clients by hand. There are Android gateways that solve the raw transport problem — a phone with a SIM sends the SMS — but they need a technical person to stand up and maintain the whole infrastructure. The client wanted us to solve that: to take the infrastructure mass-market and build the interfaces and integrations so that non-developers can find their way around with ease.
What we built
We started from the open-source gateway core — a Kotlin Android app that turns a phone into an SMS endpoint over an on-device Ktor server, and a Go service that routes messages to connected devices via Firebase — extended it, and built the whole commercial layer on top. Accounts became multi-tenant, with teams and per-location API keys. We built the dashboard non-developers actually use: a unified chat inbox, bulk campaigns with recipient groups and delivery tracking, and SIM warmup that gradually builds a number's reputation. We made it native to the tools the buyers already use — a GoHighLevel integration that registers as a custom conversation provider per sub-account and maps SIM cards to locations, so sends and replies flow through the CRM the agency already runs. For developers there's a public REST API with a JS/Node and Python SDK, plus Verification (OTP) and Contact-Tag APIs, and signed webhooks for sent, delivered, received, and failed events. Billing runs through Stripe and gives instant access. Device pairing is a QR scan; the fleet reports battery, SIM count, and connection status to the dashboard in real time. We also designed and built the client's public presentation site — the landing page that sells the product, with pricing and a setup walkthrough.
Modules & surfaces
- Multi-tenant dashboard & teamsAccounts, sub-accounts, and team members with scoped permissions. Each location gets its own devices and API keys.
- GoHighLevel integrationRegisters as a custom conversation provider inside GHL per sub-account and maps SIM cards to locations — sends and replies flow through the CRM the agency already runs.
- Bulk campaignsRecipient groups, campaign scheduling, and per-message delivery tracking across connected SIMs.
- SIM warmupAutomatically sends a controlled volume of messages per day to build a new SIM's sending reputation.
- Public API & SDKsA REST API with a JS/Node npm package and Python, covering SMS, Verification (OTP), and Contact-Tag endpoints — plus signed webhooks for sent, delivered, received, and failed.
- Device managementQR-scan pairing and live telemetry — battery, SIM count, and connection status for every connected phone.
- BillingAppSumo lifetime tiers and Stripe, gated by SIM-card limits with unlimited messaging.
- AnalyticsSent, received, delivery rate, reply rate, opt-outs, and estimated savings versus Twilio over time.
- Presentation siteThe public presentation site — landing page, pricing, and setup walkthrough — designed and built to sell the product.
How we approached it
Rather than reinvent SMS transport, we started from a proven open-source gateway and spent our effort where the product value was. First we hardened and extended the core so it could run as multi-tenant infrastructure. Then we built the commercial surface: the dashboard a non-developer can operate, billing, and — most importantly — the GoHighLevel integration, because that's where the target users already work. SIM warmup and delivery tracking came from a simple reality of this model: you're sending through real consumer SIMs, so protecting sender reputation is part of the product, not an afterthought. The developer API, SDKs, and webhooks make it something other software can build on, not just a dashboard.
Outcome
It sells as a self-serve product on AppSumo across five lifetime tiers, from a single operator to unlimited SIMs. As of writing: around 19.4M messages delivered across 3,800+ connected phones, 99.2% carrier delivery, and roughly 2.3s average send — at about $0.001 per message, close to 95% below the 10DLC competition, with no 10DLC registration.