I moved from Canada to New Zealand last year, and I wanted a way to call my family in Canada without incurring long distance charges. I found the fantastic Fongo app. This app gives me a Canadian telephone number on my mobile phone and allows me to call almost any number in Canada for free, using mobile data instead of calling minutes.
So – there's an app that will give you a Canadian number and allow you to call Canadian numbers. What apps do you know of for other countries?