Final answer:
The highest cost per contact according to HDI is through voice channels, like telephone support, due to higher personnel costs and infrastructure requirements.
Step-by-step explanation:
According to the Help Desk Institute (HDI), the highest cost per contact is typically incurred through voice channels, such as traditional telephone interactions. Voice channels often require immediate, real-time assistance from support personnel, resulting in higher personnel costs. Furthermore, costs can increase due to the necessity for telephony infrastructure and potentially longer interaction times.
Other common support channels include self-service, email, chat, and social media. Each of these has varying levels of cost efficiency, but generally, they are less costly than telephone-based support. Self-service options, for instance, can significantly reduce direct human interaction, therefore minimizing the cost per contact for a help desk support scenario.