Answering machines, whether home-based or as a cell phone calling feature, is not standardized. Therefore it can’t be detected with 100% accuracy. However, if Uncall detects voicemail, your message will play and the DashBoard status will indicate “machine.”
To guarantee your message is received, simply include a “Yes” or “No” confirmation question in your Message, such as, “Will you be able to make your appointment?”
Uncall also provides an option to “Call Later” where you specify a calling time when you think your recipient will be available to answer the phone.