What are some alternatives?
When comparing Vitelity and Signal, you can also consider the following products
Eir SIP Voice - eir SIP Voice is revolutionizing the core communications tool of business that carries both calls and data over just one connection.
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Google Voice - Google Voice gives you one number for all your phones, voicemail organized in an email format, free...
WhatsApp - WhatsApp Messenger: More than 1 billion people in over 180 countries use WhatsApp to stay in touch with friends and family, anytime and anywhere.
BVoIP - BVoIP allows to easily add Cloud & On-Premise VoIP PBX to the product offering without having to re-invent the wheel or add another layer to the daily operations..
Riot.im - Open source interoperable collaboration app.