A$($n$)\_\_\_\_$ is a service from local telephone companies in which up$-$to$-$date telephone facilities at the telephone company$$s central $($local$)$ office are offered to business users, so that they don$$t need to purchase their own facilities.

$$local exchange carriers $($LECs$)$

$$central office exchange service

$$interexchange carriers $($IECs or IXCs$)$

$$private branch exchange $($PBXs$)$