Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Google Voice - Google Voice gives you one number for all your phones, voicemail organized in an email format, free...
Sonar - 2-way chat with your customers over SMS and FB Messenger
Visible - Visible is a wireless service by Verizon that offers unlimited data for a small price and enables you to earn a few bucks by referring friends.
ThroughMessage - Uncomplicated customer chat for ecommerce websites
Fonoster - A marketplace where local telecom companies can publish numbers, developers can build voice, video, and chat solutions.