John

I suspect there are many different options, but there are certainly in the UK many cards that you can buy from small shops that allow you to make international calls for a few pence per minute - very similar to the cards I use when in the USA to phone back home to the UK (the ones I buy in the Paris LV for example let you then call a toll-free number to make the call to the UK - it is the same system when you buy a card here to make international calls). I believe this can be one of the cheapest ways to make calls.

As others have mentioned, you can also buy pay-as-you-go SIM cards to make calls from the country you are in, which is good for domestic calls but may be more expensive if you want to make international calls.

Regards

Jason