SIPfoundry is a not-for-profit open source platform for unified communications and telephony. The platform is extremely powerful, it does take some time to deploy and configure. If you are looking for a free SIPfoundy alternative, available both in cloud and on-premise (with open source code access), that requires minimal setup and is ready to use in just 5 minutes, Bitrix24 is a great choice.
Using Bitrix24 as SIPfoundry alternative
* Please note that the information may have changed since the publication. For current prices and features please visit Bitrix24 pricing page.