Truecaller - Find a person by a name or phone number worldwide for free using Truecaller.
Twilio - Brings voice and messaging to your web and mobile applications.
CallApp - Free Caller ID & Call Blocker app that allows mobile users to block phone calls, identify calls, blacklist unwanted callers and much more.
Plivo - Plivo simplifies your customer engagement.
CallerSmart - CallerSmart is an application that is basically used for the purpose of looking up mystery phone numbers for free.
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates