Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
MailClark - The Slack bot for external communications
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.
Alert.email - Get your important emails delivered to a Slack channel
Plivo - Plivo simplifies your customer engagement.
Clubble.io - Answer emails via Slack.