calling ringtonumber from SIP

we posted a while ago in the public side how to call ringtonumber from SIP. whatif you do not want to dial the extension or would like to forward a DID for free to the usa or canada. this is how. if the ringtonumber is 6417150120 and the extension is 8888 than just dial sip:6417150120x8888@freedigits.net from any sip phone and the phone asigned in ringtonumber will ring right away; no prompting extensions to enter and of course call for free through SIP.