SIP (Standard Internet Protocol) Trunking is a new technology, and the latest in Voice Over IP technology. Essentially you only need an internet T1 and an internet protocol based phone system and you can have phone numbers that you get from all over the country that will ring into you at one location. It essentially allows you to market locally all over the country from a centralized spot. The numbers are typically very inexpensive and the listings as well, especially in comparison to traditional phone services.
If your business requires a local presence throughout the country, but your calls are handled primarily out of a single location this is definitely worth looking into.