Ever phone number needs a line, physical or wireless to get to the end user. This line is also called a channel. Most DIDs by default come with 2 channels.
The number of channels you have determines how many people can call you at the same time.
Normal use would not require more than 2 channels. However if you run a business and are using the DID for the main line in your office you might have more than 2 people calling and therefore would require more than 2 channels.
Please check with us on costs for channel based DIDs.