A "ringless voicemail", or "voicemail drop", is understood as a “call” where the intention is not to ring and get connected to the “called” party but instead to connect directly to its voicemail and leave a message.
Is it possible with Twilio?
No, it is not possible to leave ringless voicemails or voicemail drops with Twilio. This practice is not supported by Twilio as it does not align with our Terms of Service and is illegal in some countries and states.
If for some reason you’re not trying to go straight to voicemail on your outbound calls but they’re going directly to it, please first check the device "blocked number" list. Voicemail functionality is not controlled by Twilio in anyway. It is controlled by the end device or the service provider for that device, so if you are facing an issue with calls going to voicemail, it is often the case that the number is blocked on the device, there's a spam blocking software installed on the device, or the service provider is filtering the call. If the issue persists, try calling from a different caller ID to confirm if the issue is specific to one caller ID.
If you have validated the device and escalated to the service provider but calls continue going straight to voicemail, please open a ticket with Twilio Support here, select the Programmable Voice product, and include a thorough description of the issue along with the testing and steps taken per the guidance above.