I was ready to give this site the worse review ever after using a different site that said 3 customers could make phone calls for 10p a minute only afterwards to find out that it was charging me like 35p, a penny cheaper than just phoning from my mobile without any codes.
Followed the instructions, and made a call from a 3 mobile (UK) to a mobile (Spain), and was charged 9p a minute as advertised. So in my experience it works.