Talkster is quite cheap as it uses a conference call bridge. This is how it work;
1) user enter the number he wants to call into the Talkster's homepage
2) then enter the phone number he is calling from. At this point, a new US number is assigned to the user's friend.
3) now the user can call him by dialing that number directly that the user can save into my address book.

How it works is that while the user is calling, an SMS is sent to his contact telling him to call the user back at a local number the user been assigned with. When the friend calls, both him and user's call are connected.

The cost to the user is very cheap as he is only paying the local call to the US number assigned. However, his contact must call back a local number which he is paying for according to his plan.