OpenPhone

It is a cross-platform mobile messaging app for iPhone, BlackBerry, Android, Windows Phone and Nokia. It allows users to send text messages and voice messages, make voice and video calls, and share images, documents, user locations, and other media.

Since RingCentral is cloud based, you enjoy the freedom to connect and manage multiple locations, devices and workers within your cloud phone system. You can easily customize users, departments, and call handling rules. No matter where you, or the users, are. You only need a high-speed Internet connection and your phone system is ready to work lightning fast, anytime and anyplace. There’s no PBX hardware.

Aircall is an app that you can install and setup in a few minutes. It lets you buy one or several phone numbers across the world, add teammates to your dashboard, and place & receive calls on your existing devices. Everything is managed inside the Aircall app.

It is an open standards IP PBX that offers complete Unified Communications, out of the box. Suitable for any business size or industry it can accommodate to your every need; from mobility and status to advanced contact center features and more, at a fraction of the cost.

It is a pure-cloud business communication platform that's in tune with the way your team works . Connect your team with a business communication platform that powers voice, video, messages, and meetings across your existing devices.