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
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.
BulkSMS - SMS messaging service provider offering two-way SMS communication services.
MobileDay - MobileDay provides one-touch access into conference calls and online meetings from iOS or Android devices.