Which option is NOT a PSTN option for Webex Calling?

In the context of Webex Calling, the cloud provides several options for connecting to the Public Switched Telephone Network (PSTN), facilitating voice services. Among the choices provided, the option that is NOT a recognized PSTN option for Webex Calling is managed PSTN.

A cloud PSTN provider typically refers to third-party services that handle PSTN connectivity through cloud-based solutions, which can be easily integrated with Webex Calling. Service providers are also an option whereby established telecommunications companies deliver PSTN services directly to customers. Premise-based PSTN refers to traditional telecommunications infrastructure hosted on the client's premises, supporting local PSTN access.

Managed PSTN, while it sounds plausible, does not specifically align with standard deployment strategies supported by Webex Calling, which emphasizes cloud and service provider integrations. Thus, this distinguishes it from the alternatives that directly facilitate PSTN connectivity.