All calls are billed in sixty-second increments, from pickup to hang-up. We bill the length of the call, and not the length of the message that you are sending. This means, for example, that messages left with answering machines will last longer than calls that are answered live. The per-minute cost of the call will depend on the billing plan that you choose.
In the case of the Cloud Call Center, the sixty-second rate is calculated from the time the agent logs in to the time the agent logs out. The billing has no relation to the number of calls the agent makes. For example, if an agent logs in at 2:00 PM, and logs out at 3:00 PM, the account will be billed for one hour of usage, regardless of the number of calls or connections that the agent made during that time.