Skype reduces an micro-multinationals phone bills to a very large extent. But if someone isn’t at their computer, you still have to call them (and pay for the international call).
Voipbuster is a web-based service that solves this problem.
It provides free 1-minute calls to many countries without a deposit. If you make a deposit of at least 1 euro with them, the 1 minute limit is removed. The US is on the free countries list (India is unfortunately not ;-<). However, free calls from India to the US are more valuable to me, since my developers don't have international lines (they are more expensive / unusual in India than in the US). In fact, even my Delhi office doesn't have an international line!
I just found out about this today. I tested it and it works. We'll be using it at uzanto: let’s see if we can completely eliminate international phone charges from our costs!