javascript
// Dynamic implementation in a VAPI workflow
async function prepareOutboundCall(customerPhone, customerId) {
  // 1. Fetch customer data and call history
  const customerData = await yourDatabase.getCustomer(customerId);
  const callHistory = await yourDatabase.getCallHistory(customerId);
  
  // 2. Format the history as structured content
  const formattedHistory = formatCallHistory(callHistory);
  
  // 3. Prepare the contextual message
  const contextMessage = `
CUSTOMER PROFILE:
Name: ${customerData.name}
Phone: ${customerData.phone}
Account ID: ${customerData.accountId}

PREVIOUS CALL HISTORY:
${formattedHistory}

CURRENT CONTEXT:
- Purpose of today's call: ${customerData.currentCampaign.purpose}
- Offer: ${customerData.currentCampaign.offer}
- Notes: ${customerData.currentCampaign.notes}
  `;
  
  // 4. Create or update the assistant with this context
  const assistant = await vapi.assistants.create({
    name: `Outbound to ${customerData.name}`,
    model: {
      provider: "openai",
      model: "gpt-4-turbo",
      messages: [
        {
          role: "system",
          content: "You are a voice assistant making an outbound call to a customer. Use the provided call history to personalize the conversation and provide continuity of service."
        },
        {
          role: "user",
          content: contextMessage
        },
        {
          role: "assistant",
          content: "I will use this context to provide a personalized experience."
        }
      ],
      temperature: 0.4
    },
    firstMessageMode: "assistant-speaks-first",
    firstMessage: `Hello, this is ${yourCompany.name} calling for ${customerData.name}. Is this a good time to discuss your service options?`
  });
  
  // 5. Initiate the call
  return vapi.calls.create({
    from: yourCompany.phone,
    to: customerPhone,
    assistantId: assistant.id
  });
}

// Helper function to format call history
function formatCallHistory(callHistory) {
  return callHistory.map((call, index) => {
    const date = new Date(call.timestamp).toISOString().split('T')[0];
    return `
Call #${index + 1} (${date}):
- Purpose: ${call.purpose}
- Main points: ${call.summary}
- Customer concerns: ${call.customerConcerns}
- Action items: ${call.actionItems}
- Outcome: ${call.outcome}
`;
  }).join('\n');
}