ringtonumber hack for free calls to USA

ringtonumbers forward to any phone in USA(and maybe canada) based on
dialing on number in iowa and than entering a 4 digit shortcode.

i have discovered that the access number can also be called via sip by dialing 10digitringtonumber@talkdigits.net.
you will than be prompted to enter the shortcode and be transfered to
the cell phone or landline free of charge. you can also call a
sipbroker number and use the talkdigits prefix(*8404) in front of the
10 digits ringtonumber and than the short code when prompted to
connect. ringtonumber does not do verification; so you can change the
destination number to any number you want to call. this basically
allows free calls at local cost from any place with sipbroker to any US
phone number.

cheers