One switch, voice mail system, and paging terminal costs less than two. Not everyone realizes, however, that variable expenses are lower for larger messaging services than smaller ones. The statistics of telephone call traffic dictate that the bigger you are, the more efficiently you use operators, equipment, and trunks. This is due to the averaging effect of telephone traffic coming from large groups of callers. In a large group, each operator or voice mail port can handle more calls on average.
Callers have a lower probability of waiting on hold or getting a busy tone.
Airlines, credit card companies, and insurance companies learned this a long time ago. Reducing payroll and overhead costs is the reason that customer service operators for these high-volume companies are typically at one large site in the country.