A simple question but I have not been able to find the answer.

I have the skype app on my iphone. Can I use skype credit to call UK landlines and mobiles from my iphone when I am abroad and if so do I need to have a wifi connection or will it work with 3g? (I usually disable 3g connection when abroad as I am afraid of running up huge bills). What are the cost implications of using 3g connection abroad?

Thanks for any advise you can give me

Frank