[andy]

For people who want to make absolutely loads of int'l calls from the UK, there is an add-on on 3 - £15 buys up to 3000 minutes in a month to 23 countries.

Or another option on 3 has free Skype calls, which could also sidestep the cost to some people calling you. SkypeIn and SkypeOut are not supported on this though, and not all phones