Channels (sometimes referred to as sessions or trunks) are the network capacity that has to be purchased in order to receive calls on your DID numbers. Each channel allows for one concurrent call.
Trunk Zones: Channels are available in 4 different trunk zones : zone A, zone B, zone C and world zone . Each zone A, B and C allows you to add numbers from multiple countries around the world. Call capacity in each zone can be shared by numbers from countries within the respective zones. The world zone channels allow you to add numbers from any country.