Over the past year during various conversations with telecom insiders including analysts and reporters there always seemed to be a question about CPaaS from UCaaS providers.
At the present time, Twilio is likely the most commonly known CPaaS provider, quickly followed by Nexmo, which Vonage acquired. Plivo is another, and even Bandwidth.com has their own version of CPaaS they offer and Ribbon, the marriage of Sonus and GenBand offers KANDY. Even former client OnSip has their own CPaaS platform.
In a nutshell, CPaaS provides a platform for custom development of applications and services that can hook into your telecom provider via an open or private API. If you use Zapier or IFTTT for app automation, think the same way about CPaaS.
As CPaaS gets more understood watch as enterprise developers begin to look more at it, to enable their telecom and collaboration services to do more that the carrier doesn't yet do.