A call path is one call that can be handled on a hosted service. In many services, this equals the number of users/extensions/lines of service. In some offerings, they may be separated. In an example of this case, a customer can make 1000 extensions to provide employees. But they are only able to manage up to 300 phone calls at a time. They don’t expect to ever have to field more than 300 calls at the same time. The extra extensions may be for better reporting on who takes calls.