You want actual, International phone calls? How quaint. And expensive. If you don't have them already, get a couple of used Android phones for less than a hundred bucks each. Check them at willmyphonework.net
Then have your wife pick up a data sim in the other country. Now you two can use viber or a similar chat app. If you are both connected to Wi-Fi, then you can do all of the following for free with viber:
1) voice calls
2) VIDEO calls
3) Text chat
But viber requires registration to an actual, activated smart phone (iphone, android)
As for how often? I think your question is rather curious. In most relationships, the wife is the chatty one. I know when my wife goes out of the country, she is texting me constantly.... (which is kind of annoying)
In the unlikely event that you don't get text or voice call or something from your wife all day, then definitely call her, voice call. But during the day, you can send her a few short texts to let her know you are thinking about her....
Just don't send more than a few texts in a day, especially if she hasn't responded to them. And try not to call more than once a day.