I don`t know about phoning the States for free, but my wife spends over an hour every Sunday ringing our Daughter in Texas at Two and a half pence per minute with "SuperLine". Most of our UK calls are covered by a £10 a month standing charge . There are a mass of other firms some cheaper but Superline have been trouble free now for 4 years and I am loath to change .
I have used Telediscount for some years (click here) very efficient, and you do not need to set up an account as you are billed through your normal BT telephone account, shows as a call to an 0844 number.
I have phoned Germany (1p per minute, Austria and Hong Kong (both 2p per minute) over the Christmas period and no problems whatsoever.
Just checked the site and USA calls currently at 1p per minute
I think some of you missed the point of the question raised by sea princess XP Pro. She wanted to have a free source of finding telephone numbers in the USA and Germany. In my opinion the BT charge is exorbitant.
Low cost calls are available; I personally use either 18866, 18185 or Telediscount, depending upon which rate is best.