Skype™ open its SIP Protocol

Skype™ launch its beta version of SIP (Session Initiation Protocol), to allow companies and offices that own a PBX, a telephone exchange like Asterisk, to use the cheap rates of Skype™ to call telephones all over the world, obviously the Skype-To-Skype calls, by the SIP protocol, are free.
In a near future it will be possible to knock down almost completely the costs of normal phone calls, when most companies, offices and business activity will be equipped with easy and practical systems of voice communication by Internet, without the need to use a phone provider, if not for the broadband connection.
A defect is that the dispatch of normal fax is not still supported by the SIP protocol and it still need the use of a normale telephone line, even if soon, supposedly, the fax will be substituted by the Certified E-mail.