We detect voicemail using heuristic algorithms which are based on the tone of voice, the speed of spoken words, etc. This detection usually takes 3 to 5 seconds and usually has an accuracy of 60-75% which is on par with the industry standards. You can enable AMD at Plivo using our outbound call API with the machine_detection and machine_detection_time parameters. For more information, see our outbound call API page.
To increase the accuracy of the machine detection, you can setup the machine detection method as asynchronous and increase the wait seconds (machine_detection_time: is the time allotted to analyze if the call has been answered by a machine. It should be an integer >= 2000 ms and <= 10000 ms. The default value is 5000 ms.)