The easiest and most basic idea would be to use one’s phone. Shoppers would enter the visit scenario prepared and set the phone on record to be able to capture the audio of the whole visit.
There are programs that require the shopper to perform a call audit, instead of a visit. In this situation, shoppers can use apps, Skype recorder or any other means of recording the call.
All other aspects of an Audio Recorded Mystery Program, would follow the same as the Traditional method of Mystery Shopping. Audio is the only additional feature. In theory, it would be simple. Set the device to record and begin the visit.