If you live in the UK and want to call overseas then you are usually better off not using your usual phone service provider, but instead there are dedicated websites with cheap rates and here are just a few:
Overseas calls from the United Kingdom
Cherry-call – Calls cost just 1p per minute to the US right now! (this 1p per minute applies to both landlines and mobiles within the USA)
Cheery-call – Calls cost just 1.5p per minute to Australia right now to landlines in Australia and 6p per minute to mobiles.
Joy telecom – Calls to the USA from the UK for just 3p per minute (for both landlines and mobiles)
Joy telecom – Calls to Australia from the UK for just 3p per minute for land lines (15p per minute to mobiles)