I mostly use Skype but if a student wants,I can use Google Hangouts or even WeChat phone.

I use Skype, Wechat, QQ, Line, Firefox Hello, Hangouts, and Linphone. I have also used Kakaotalk before. My favorites are those software which are open source. Like Ekiga Softphone, Linphone and Firefox Hello. Firefox Hello is awesome just not yet very well known. So becaues of the social inertia I have to use Skype. I don't like this. There are awesome open source software that are free and deserve a look.

i didn't use Skype before I came here～ but now I apply for a Skype ID