I Built a $2000/Month AI Phone Assistant Using OpenAI's Realtime API (Tutorial + Code)

I made $2000 last month from three local businesses using AI phone assistants built with OpenAI's new Realtime API. Here's exactly how I did it -- and why this might be the easiest way to monetize AI in 2025. Most small businesses still suck at answering their phones. They miss calls during lunch, after hours, or when they're swamped. That's where voice AI comes in, and OpenAI just made it stupidly simple to build. Why the Realtime API Changes Everything Before this API, building voice assistants meant juggling speech-to-text, GPT calls, and text-to-speech separately. It was clunky and had noticeable delays that made conversations feel robotic. The Realtime API handles everything in one WebSocket connection. No more awkward pauses. No more "processing your request" dead air. Just natural conversation flow that actually sounds human. I've tested it against competitors like Vapi and ElevenLabs' conversational AI. OpenAI wins on latency every time. Sub-300ms response times are now standar