Ninja Number is described as 'second phone line that works on your smartphone and provides the leading edge solution for business owners to manage inbound communications economically, efficiently, effectively and effortlessly' and is an app in the Social & Communications category. There are three alternatives to Ninja Number for a variety of platforms, including Android, Online / Web-based, Windows, Mac and SaaS. The best alternative is RingCentral. It's not free, so if you're looking for a free alternative, you could try CallHippo.
Zadarma is an international VoIP provider with over 13 years of experience and 1.5 million registered users. It offers virtual numbers in 90 countries, Free Cloud PBX, free website widgets and call tracking and free integrations with top CRM systems.
CallHippo is a Virtual Phone System which allows businesses to buy instant phone numbers from over 50+ countries around the world. With our easy to use interface and robust backend any business can set up their phone system in less than 3 minutes.