Founding Engineer at AgentPhone

About AgentPhone

AgentPhone gives AI agents phone numbers. Voice, SMS, and iMessage through one API.

The oldest address on the internet is a phone number. Every business, every bank, every human still runs on it. But the entire telephony stack was built for humans dialing humans. AI agents are about to make and receive millions of calls and texts, and the infrastructure underneath them was never designed for that.

We're building it. Over 100 companies use AgentPhone today to provision numbers, place and receive calls, send texts and iMessages, and stay compliant with carrier regulations, all from a single API and MCP server. We're backed by Y Combinator (P26) and investors including Swift Ventures, Singularity Capital, Leonis Capital, Rebel Fund, Pioneer Fund and more.

The Role

You'll be our first engineering hire, working directly with the two founders (CEO and CTO, also brothers, we argue efficiently). Your job is to make the company better every single day: better product, better infrastructure, better customer experience. You'll ship code, talk to customers, and own problems end to end.

You don't need any telephony experience. Telecom is a weird, adversarial, undocumented world. Carriers filter messages with rules they won't publish. Countries block traffic at the network level. Apple decides your iMessages are spam and won't tell you why. Nobody comes in knowing this stuff. What we need is a go-getter who can use AI extremely well to learn fast, ship fast, and figure things out that most companies gave up on decades ago. That's the moat, and you'd be building it.

What You'll Do

• Build and scale core telephony infrastructure: SIP trunking, real-time voice (LiveKit), call routing, and media handling
• Own messaging delivery across SMS, iMessage, and RCS, including deliverability debugging when carriers silently drop traffic
• Ship developer-facing surfaces: our API, SDKs, MCP server, webhooks, and dashboard
• Build compliance infrastructure (A2P 10DLC, TCR registration, KYC) so customers don't have to think about it
• Talk to customers directly and turn their problems into features, sometimes the same day
• Set the engineering foundations (testing, CI/CD, observability, on-call) that every future hire inherits

Who You Are

• A go-getter. You see a problem, you own it, you fix it, no one has to ask
• You use AI tools extremely well and move faster with them than most engineers think possible
• You've shipped real software that people actually use
• Comfortable talking to customers directly and turning their problems into product
• You move fast in ambiguity and take full ownership without process or specs
• No telephony experience required. We'll teach you everything, or you'll figure it out with us

Nice to Have

• Experience with telephony, VoIP, SIP, WebRTC, or messaging infrastructure (Twilio, LiveKit, Bandwidth, etc.)
• You've built AI agents or worked with LLM APIs, MCP, or voice AI stacks
• You were one of the first engineers at a seed or Series A startup
• Developer tools or API product experience

Interview Process

1. 15 min call with the CEO
2. 45 min technical interview with the CTO
3. Paid work trial: build something real with us for a day or two (we'll fly you out if needed)

How to Apply

Send us a short note with:

• The hardest technical problem you've solved and how
• A link to something you've built (GitHub, product, demo, anything)