How to make your own phone 2 phone free

I've seen many foreign bloggers recommending this thing recently: jajah! I'm not sure how to pronounce this word yet; I call it "jiajiahaha"! It's a free service for mobile-to-landline, landline-to-landline, and mobile-to-mobile calls. In foreign countries, such services may not be particularly impressive, but the key is that this service can also be used in mainland China.