Uttero is a voice channel that lets Claude Code take and make phone calls during a coding session. An incoming call arrives as a channel notification; Claude hears the caller's transcription, speaks back via TTS through the `reply` tool, and keeps editing your codebase between turns. Works like a live collaborator who happens to be on a phone line. Tools exposed: reply (speak), call_user (outbound), end_call, list_calls. Audio, transcription, and TTS are handled by Uttero's hosted backend (api.uttero.dev). The plugin itself is ~500 lines of TypeScript that speaks MCP stdio and authenticated HTTPS. Credentials are stored locally at ~/.uttero/credentials.json (mode 600) and never shared with callers. The plugin deliberately omits `capabilities.experimental['claude/channel/permission']` so voice callers cannot approve Bash/Write/Edit tool use.