The invention provides a system, method and apparatus for connecting a target telephone with Voice Mail System in a network comprising Centrex or other TDM telephones and VoIP (or SIP) type telephones. The invention provides a system for the connection of a target telephone with a Voice Mail System in a network using a protocol converter that is connectable to a PSTN network and an IP network and a voice mail system. The converter may comprise instructions; computer memory and a processor. The converter converts message signals between SIP signals and SMDI signals as may be required and then directs the message signals to a target telephone, which may be through an IP Gateway. The system may further comprise a management console or an end office facility. An Electronic Numbering facility comprising phone numbers convertible between PSTN numbers and SIP numbers may also be provided with the system.