If you’re on the Free plan, you’ll have to head to the dashboard to buy numbers. The Developer and Enterprise plans both come with numbers included in the subscription. For more info, see Pricing. 
phone_number = vocode_client.numbers.buy_number()
You’ll get a response that looks like: 
{
  "id": "***",
  "user_id": "***",
  "number": "11234567890",
  "inbound_agent": {...}
}
Your phone number is now active! Call the phone number and have a conversation with your AI.