TextNow - TextNow is a mobile virtual network operator (MVNO) that provides a free phone service to users by using other cellular networks coverage.

Twilio - Brings voice and messaging to your web and mobile applications.

TextMe - TextMe is a free calls and messaging application at both local and international levels.

Jasmin SMS Gateway - Jasmin is a very complete open source SMS Gateway with many enterprise-class features such as:

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.

Skype - Stay in touch with your family and friends for free on Skype. Download Skype today to chat and call on desktop and mobile.