Let’s say you live in Dallas; you have asterisk PBX system, an internet connection, and four local phone lines (PSTN) in your office. However, your four local phone lines have the ability to call anywhere in Dallas free of charge. However, If you were to install four analog ports onto your asterisk PBX, you could then connect your four local lines directly into your asterisk system. Further, it also connects your asterisk system to the internet, you would then have the ability to terminate four simultaneous calls into the Dallas Local Area. Therefore You would then be a termination provider for the Dallas area. You can change the rate of $.005 cents per minute, saving others money while making a few bucks yourself.
However legally, you would have to check the rules in your local community about using your local lines in this manner, but this is nothing new for local companies to date.