Pinger

Pinger, Inc. is a US Telecom provider for free texts, pictures, calls, and voicemails. Pinger was founded in 2005 by former Palm, Inc. managers Greg Woock (CEO of Pinger, Inc) and Joe Sipher. The company was founded in 2006 and is headquartered in San Jose, California. Pinger is funded by Kleiner Perkins Caufield & Byers, DAG Ventures, Deutsche Telekom, and T-ventures and has raised US$18.5M.
Products.
The company has released several apps, mostly being available on iOS, Android, Microsoft Windows and Macintosh.
Textfree.
Textfree is an app that allows user to call and text using a real phone number for free. The app has a free ad-supported version and a paid version. The app allows you to text anyone in the world.
Sideline.
Sideline is an app that adds a second phone number to your phone using technology similar to Textfree. It's available for iOS, Android, Microsoft Windows and Macintosh. Their official website is sideline.com.