I have just switched phone service provider, and now use
http://www.18866.com - amazingly cheap service. Register online with a CC, and your bill is online. Then all you do is precede the number to be called with 18866. Calls to other countries can be made for as little as 1p per minute - the USA is 1p per minute at any time in the 24 hour day. When making the call, before being connected a voice tells you the charge rate that will apply.
I called Lazs! We talked for 53 minutes.

Checked the online bill afterwards - sure enough - 53p.
