Google Voice - Google Voice gives you one number for all your phones, voicemail organized in an email format, free...
Callmama - Get cheap international calling, international virtual number, Call Mama Gives an added advantage to send message and make calls to non-user of Callmama App.
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.
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.
KrispCall - Virtual cloud phone system for business