Can I make free long distance VoIP calls with asterisk.org software?
Asterisk can assist you in making free or very inexpensive long distance calls.
The question is fairly broad.
For making long distance phone calls to anyone on the PSTN (public switched telephone network) you will need a VOIP service provider to interoperate with Asterisk. Prices and availability of these services vary.
Alternatively, if you only make long distance calls to a fixed number of locations, ie) satellite offices you can configure Asterisk to communicate between these locations via VOIP directly without a service provider. This type of setup has many possible configurations and requires enough bandwidth between sites.