Bandwidth's BXML provides an alternative to its Voice API for handling operations on active phone calls, facilitating the implementation of two-factor authentication (2FA) systems. While the Voice API is used to initiate calls, BXML operates through hosted server endpoints accessed via HTTP GET requests to manage call interactions. In a 2FA setup, the registration process involves confirming phone ownership by requiring users to enter a code visible only on the registration page, while the login process uses a phone call prompt to finalize authentication. Security is a concern since BXML can be accessed by knowing the endpoint URL, so protective measures, such as requiring credentials for requests, are recommended to prevent unauthorized access. Although BXML and API calls offer similar outcomes for users, developers experience distinct interactions with their servers when using these tools.