Google Voice - Google Voice gives you one number for all your phones, voicemail organized in an email format, free...

Phonebot - Make phone calls from within a Slack channel

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

ShareAccount - Share your account without giving out your password

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.

Wing-project.org - WING - Wireless Mesh Network for Next-Generation Internet