AT&T and some of the CLECs like Windstream offer a product called Centrex that might be what you're looking for. In terms of reliability and call quality, it's

AT&T and some of the CLECs like Windstream offer a product called Centrex that might be what you're looking for. In terms of reliability and call quality, it's pretty much at the top of the stack. Generally speaking, you have to call for pricing, though.