@Shashank-I saw a demo at FOSS.IN/2005 where the guy made a call from his lappy to his office in the US! There are lot of things to be done before you can do that. The official forum might help you out in this.
@Nucleus-Asterisk mainly acts as a software PBX and can also act as a point for VoIP calls. Consider an example of an office(again). When you want to call your colleague in another department, you just lift the phone and dial the internal phone number. Your call is switched internally. In case, you need to make a call to your house, you usually have to press a number, like zero. When you do this, the PBX allows your phone to switch to the extenal telephone exchange, i.e., the exchange from where we get the telephone connection. In commercial hardware PBX, it costs a lot for the equipment and maintenance, whereas Asterisk does the this and a lot of things for free!
In an article, on Linux For You, the author had setup Asterisk so well, that calls would switch to a particular family member's room if his friend/acquintance call. First, the caller is greeted with a welcome tone, which is recorded by the author, then the caller is asked to press a number to reach a particular member of the family. In another configured feature, if you wish to block telecallers, you put the number on the list and in case they call back, the phones doesn't ring at all, but it just hangs upon the telecaller!! There were lot more things which he had done. I don't remember all of them. I found these 2 to be the coolest. Ofcourse, you can use Asterisk as an answering machine
You can read a one of the many success stories of using Asterisk at home
*www.chrishardie.com/weblog/archives/2007/10/my-voip-home-phone-setup-using-trixbox.html
