I am interested in this product.
Can I just buy phones of you and put this software on any computer and I have a phone system for a small company?
If I am understanding this correctly could you provide me with diagrams of a possible setup solution?
Yes . Asterisk is free and opensource . You will find installation document by a simple googling . You should read "Asterisk The future of Telephony " book .
Asterisk: The Definitive Guide is the current revision of “Asterisk: The Future of Telephony”