HP OpenCall is an extensive portfolio of network and telephony products offered by the HP Software Division of technology company HP. It is most commonly described as a suite of software and hardware applications which allow implementation of common telecom operator services such as voicemail, sms (short message service), prepaid, billing, hlr, etc. It implements industry standard telecom protocols and standards such as SS7, ISUP, TCAP, SIP, MRCP, RTSP, VoiceXML, to name but a few.