Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
Skype for Slack - Move your slack discussions to a group skype call
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.
Aircall Now - Make voice calls inside Intercom Messenger 📞💬
Plivo - Plivo simplifies your customer engagement.
Calls on Slack - Make voice calls in Slack