curl https://api.vozagent.ai/v1/phone-numbers/pn-a1b2c3d4... \
  -H "Authorization: Bearer <token>"

{
  "id": "pn-a1b2c3d4-e5f6-a7b8-c9d0",
  "phone_number": "+15551234567",
  "label": "Main Line",
  "provider": "twilio",
  "status": "active",
  "assistant_id": "a1b2c3d4-e5f6-a7b8",
  "outbound_assistant_id": "b2c3d4e5-f6a7-b8c9",
  "sms_enabled": true,
  "monthly_cost_cents": 200,
  "last_used_at": "2024-01-15T10:30:00Z",
  "vapi_phone_number_id": "vapi-pn-xyz123",
  "created_at": "2024-01-10T09:00:00Z",
  "updated_at": "2024-01-15T10:30:00Z"
}