Cheapest call option from Canada to Mongolia Cell? (Ulaanbaatar)

I live in Canada right now. My soon-to-be-wife and kid are in Mongolia. Their internet connection is really bad; out of a week, we probably have only a night or two of good connection. So Skype or any kind of VOIP call isn't an option here.

I used to use Skype Protected content bundle which is around 12 cents per min, but we burned it out pretty quick and it's not recurring until the next month. Too bad though, I found Skype call quality the best so far. Right now, I'm using Vonage. It's 7 cents per minute and I can add more credit any time from my iTune account.

I wish there was an unlimited call to Mongolia from all these provider, though. I've heard from a Mongolian that I can purchase a Mongolian number and then access it through an Internet. Is that true? And how to set that up? Or is there any other way to make a cheaper call to Mongolia?