Your friends probably created an iTunes account in another country and used that to get the app. Ask them. It's a fairly common practice.
If that is what they did:
You'll need an email address (plausibly from that country).
An address in that country. Some people report using an Apple Store's address in that country.
If you have a credit card from that country, it's easy.
If not, then you need to follow these steps to create an account with out a credit card, and use iTunes Gift Cards to buy any non-free apps or content.
Creating an iTunes Store, App Store, iBookstore, and Mac App Store account without a credit card
The U.S. is popular and the best stocked, though for some specialty apps, like the BBC stuff, you may need a U.K. account.
Since I don't do this myself, all I'm doing is passing on information. I may very well have some minor details wrong. Also, there is no official support for using multiple stores, as far as I know, so you do this at your own risk.