 Most modern PBXs support VoIP.ISDN PBX systems also replaced some traditional PBXs in the 1990s, as ISDN offers features such as conference calling, call forwarding, and programmable caller ID.As of 2015 ISDN is being phased out by most major telecommunication carriers throughout Europe in favour of all-IP networks, with some expecting complete migration by 2025
Originally having started as an organization's manual switchboard or attendant console operated by a telephone operator or just simply the "operator", PBXs have evolved into VoIP centers that are hosted by the operators or even manufacturers.