Twilio - Brings voice and messaging to your web and mobile applications.
Google Voice - Google Voice gives you one number for all your phones, voicemail organized in an email format, free...
CallHippo - Easy to use Phone System with World-Class Support
TextMe - TextMe is a free calls and messaging application at both local and international levels.
RingCentral - RingCentral is the leading provider of cloud-based communications and collaboration solutions for small business and enterprise companies
Talkatone - Android App on. Google Play. Stop paying for cell minutes, texts & landlines; Turn your iPad or iPod touch into a phone; Call/Text even in areas with bad cell coverage; Call/Text when travelling without paying for expensive international minutes.