What app you americans use for personal conversations?
Here in South Europe people mostly use Viber.
Edit: I was very unaware about situation in Southern Europe as I've learned from this post...
Most people in Croatia use Viber!
I was surprised to read that a country in South Europe mainly used Viber. I'm not European but I'm almost definite that WhatsApp has the largest market share for chat apps in all of Europe. Maybe Telegram coming a close second