The Additional Voice Capacity product relates to the number of minutes per agent that a customer is allotted per month. This concept is known as Fair Usage Allotment:

Fair Usage Allotment: For no additional charge, Customer is allotted 4,500 minutes per month for each unique Agent using Inbound Voice and 6,500 minutes per month for each unique Agent using Outbound Voice (“Agent Allotment”).  A unique Agent using both Inbound and Outbound Voice is allotted 6,500 minutes per month.  Customer’s Total Fair Usage Allotment for a month equals the number of unique Agents times the Agent Allotment (either 4,500 or 6,500 minutes per Agent, as applicable). 

The Additional Voice Capacity product enables you to increase your standard Fair Usage Allotment. 

For additional information, see Voice