Skype for Slack - Move your slack discussions to a group skype call
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Calls on Slack - Make voice calls in Slack
Intercom Facebook integration - Read, manage & respond to Facebook messages from Intercom
Pingly - Your communication hub — Email, text & voice in one app
Crypton.sh - SMS - Secure Anonymous SMS in the cloud (and a phone number)