Many companies advertise a separate number that can be used when calling from abroad - This usually begins in the format +44 - There is nothing to stop you using this number from the UK (as it is a normal rate telephone call), and will be included in any inclusive minutes provided by your landline or mobile phone provider. Many others will give you a standard number if you ask.
This site is all about listing these numbers, saving you money, without having to pay additional charges. To get started and find a particular number, please click on the 'Search to find an alternative number' link at the top of the page.