Twilio Functions are used to handle the logic of selecting the best FROM number for outgoing calls, validating the TO number format using Twilio Lookup, and initiating Studio Flows to deliver 2FA codes via voice. A two-factor authentication solution can be built using this approach. The solution involves deploying a Twilio Serverless service that handles incoming requests, validates the TO number, selects the best FROM number based on country code, regional number, and default phone number, and initiates a Studio Flow Execution to deliver the 2FA code. This solution is relevant to any use case that needs to initiate outgoing calls and can be customized further for specific requirements.