CALLR - CALLR is an extremely helpful app for those who have to deal with call control protocols for their business. You can create a customized call control system that will perform a wide range of functions.
Twilio - Brings voice and messaging to your web and mobile applications.
MeetingMogul - Join any conference call with one-touch
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
CamCard - CamCard reads business cards and save instantly to phone Contacts.
Plivo - Plivo simplifies your customer engagement.