Here's how it works.
My folks in the States call a toll-free number.
When the number connects, they dial either:
+ a PIN number (if calling from a phone other than their own - I think you can set up to three numbers as "home" numbers - I chose my parents' landline, their mobile, and my sister's mobile) then my number, or,
+ if calling from a "home" number, they just dial a pre-set shortcut (to reach my landline, it's #-1-0). The call is charged per minute against the prepaid credit in the account - so as long as there is credit in the account, they can call anywhere in the world (including long-distance in the US).
So if my mom's calling from home, she'd dial 1-800-xxx-xxxx, then wait for a connection, then #-1-0. Then I answer! If she's at a friend's house and using their phone, she'll dial the same 800 number, then the PIN (10 digits - ours is our home number plus four digits, so it's easy to remember), then 011 44 xxxx xxx xxx (our landline).
So, to answer your question - there is one toll-free number, for your personal use, that enables you to call anywhere in the world. It's different from what I use over here, which is a 0844 access number that links back to my BT landline (and therefore I have to call from my landline to get those rates).