What is the cheapest way to call Ukraine?

I have family in Ukraine and I'm trying to find the cheapest way to call them.
I have an unlocked iPhone that I can use.

Cell phone and internet

Add international calling to your plan. I think some places have it for $5 a month.

DON'T call collect. Ever. I called my mom for 10 minutes and it cost over $50, where if I had just called her without collect it would have only cost a total of $3.

Skype or use an international pre paid calling card

I thought that everybody knows about Skype already. But in the same time, it is quite possible that there's no internet in the family where you are going to call (they can live in village or something).
There are two possible ways for you to call your people right now for cheapest money. First one ( you have internet plan on your smartphone or good internet via wi-fi) you just add some money to your skype account and call to their phone number in Ukraine. It is very fast. Please consider time difference.
Second way, even cheaper one, but you should write them email and arrange date and time when their smartphone has access to free internet ( no problems for big cities - McDonalds with free wi-fi on every conor) and you call each other via internet skype only for free of charge.
But hey! There's some trick in your question, right?