Skype for Slack - Move your slack discussions to a group skype call
TextNow - TextNow is a mobile virtual network operator (MVNO) that provides a free phone service to users by using other cellular networks coverage.
Aircall Now - Make voice calls inside Intercom Messenger 📞💬
Dingtone - Dingtone is a free call and texting application for making unlimited calls and text messages to any number at the moment registered in any part of the world by any cellular company.
Calls on Slack - Make voice calls in Slack
TextMe - TextMe is a free calls and messaging application at both local and international levels.