Bitrix24 is free call center software unlike any other. If you choose
cloud version you can start calling and receive phone calls within minutes. You pay only if you
need to have more than 12 employees, want to rent a phone number, SIP connector or use Bitrix24 telephony for outbound calls.
You can also purchase self hosted editions of Bitrix24 if require source code access or
would like to deploy Bitrix24 on premise.