Asterisk is a complete PBX in software. It provides all of the features you would expect from a PBX and more. Asterisk does voice over IP in three protocols, and can interoperate with almost all standards-based telephony equipment using relatively inexpensive hardware. Asterisk provides Voicemail services with Directory, Call Conferencing, Interactive Voice Response, Call Queuing. It has support for three-way calling, caller ID services, ADSI, SIP and H.323 (as both client and gateway). This is a EOL Long Term Support version. It bacame security fixes only on 2022-10-09, and EOL on 2023-10-09. For more information about Asterisk versions, see https://docs.asterisk.org/About-the-Project/Asterisk-Versions/