Yesterday I met with IDEA2, a PAAS company that allows anyone to build an integrated app in a short time. All the elements are built into the platform including API integration with a number of software apps, like Salesforce and Slack.
Slack is one of the fast growing apps. One million users log on each day. Slack is a workflow app. There's a story behind it. This company raised a chuck on money - about $25M - to build a game. After burning through $19M they realized it wasn't going to happen. However, the platform that they used to communicate and collaborate (and manage workflow) is Slack.
In the market of VoIP, integrations are key. Think about a Slack integration.