A combination of them all. I use Skype a lot as I changed countries and international calls are so expensive. I try to call some of them from time to time, though. On birthdays, for instance, I would rather call than write an email.
For local family it is by phone or SMS. For my friend in the USA I email frequently because I always have so much to tell him but I do phone him about every 3 months as it's cheaper for me to do this on the Telstra plan the home phone is on.
Only by email, but our youngest daughter hardly ever answers my emails, with the answers to the questions I ask her, in the emails, so I do have to phone her for the answers sometimes, if it's really important! I've only sent 2 txts, about 4 years ago, & have never used other social media.