Keeping in touch while living in South Korea

WhatsApp is indispensable!  I have a Korean mobile phone (I don't even bother with a landline) with "unlimited data" (11GB/month at highest speed, then 2 GB/day at a lower data rate).  I will also use Facebook Messenger with people who, for whatever reason, don't have WhatsApp.  I speak to my parents using Skype.

I call my wife in the U.S. daily, my kids a few times/week and my parents about every other week.  As for the time difference, I just schedule my calls for times I know they'll be at home, for my parents, I call fairly late in my night (their morning) and for my wife I call in my early afternoon (the end of her day).  We're about to go through a time change (Daylight Saving Time ends in the U.S.), so it may introduce some minor annoyances as to when I can call my family.

Again, I don't have a land line, so I don't make international calls, I can't comment on that.  My mobile phone doesn't allow for international calls to be made, so it's just the phone apps for calling internationally.