Welcome to the Newschoolers forums! You may read the forums as a guest, however you must be a registered member to post. Register to become a member today!
When I was abroad I used Viber for pretty much everything. You can make calls and send texts over WiFi. Skype works well too, WhatsApp is good, but you can only text.
There's also Talkatone which allows you to call any number. So if you're parents have a landline or a non smartphone you can call it rather than having to use the app and be limited to calling only those contacts.
Just download a few of those apps and tell your parents to get at least one.