Service Provider Networks

• A service provider may be able to route your call over its own system if the receiver is one of its customers. If not, part of the call may cross the "Public Switched Telephone Network"---or PSTN---in order to reach the network of the receiver's provider. This passage over the telephone network has to be paid for.
  
  

Carrier Cooperation

• Service providers are cooperating to exchange VoIP calls over the Internet rather than requiring that they be received over the telephone system. This collaboration is called "Peering".
  
  

Peering Implementation

• Peering represents a small percentage of VoIP calls and is almost entirely a service offered to corporate customers. Private customers are harder to cater to where the receiver of the call is more likely to be a land line.
  
  The public telephone companies have the advantage of being the first call for householders wanting a telephone in their homes. The established tradition of looking for someone's number in the telephone directory is a hard habit to break. Peering will increase for the domestic market as consumer attitudes and cultural practices adapt to the presence of the Internet.