Dear Sir,
Asterisk is a free pbx used for small voice over IP business...This PBX is used to make VOIP calls between registered extensions or for making long distance calls...Calls between registered extension are free calls...Means you can install the Asterisk server on one of a company servers connected to the company network, create extensions on it like 555 or 666 or whatever you want...Now in order to make calls (Local calls) you can connect any VOIP device to the asterisk server network...This device will use one or more of the extensions already created on the asterisk server in order to make local free calls with another device...If you asterisk server has a Public IP address then you can connect any VOIP device on the internet and make a call to any other device registered on the Asterisk...
Asterisk PBX could be used for making long distance calls, like calling a cell phone or fixed phone line...This could be done by dealing with one of the VOIP companies that owns gateways with PSTN network
Please fell free to ask any question you want
Regards
