Depending on the European country it is a mix of many apps, regarding my contacts:

With the friends in DACH region it is mostly about Whatsapp.

With the friends in Portugal it is mostly about Whatsapp and Skype.

With the friends in Balcans and east mediterrian it is mostly about Whatsapp and Viber.

With all of them, we still exchange plenty of SMS, as everyone has plenty of free ones on their pre-paid packages.