WhatsApp in SXM

WhatsApp Calling lets you call your contacts using WhatsApp for free, even if they're in another country. ... WhatsApp Calling uses your phone's Internet connection rather than your cellular plan's voice minutes. Data charges may apply.

https://www.whatsapp.com/

All my contacts in SXM use Whatsapp!

Been using it for a few years. All you need is WiFi. Any contacts on your calling list will show up on your whatsapp contact list if they have the app. Great for texting, calling and video calling.

Assuming you have an internet connection

I use it with Barbara all the time!
Cheers
irina