AP-N1-GSM8S4 GSM VoIP Module is a new 8-Port GSM Module (4 SIM card slots per a GSM Port) for GSM Call Termination Service. AP-N1-GSM8S4 GSM VoIP Module can be installed in our next generation large capacity AddPac GSM Gateway AP-GS5000. This GSM VoIP Module supports Quad-Band (850/900/1800/1900MHz) GSM frequency, Four(4) SIM card slots per a GSM port, Hot-Swap Switch Button, two(2) GSM Antenna Interface. This GSM module has thirty-two(32 = 4x8) GSM SIM card slots internally. Also this module supports the Voice DSP for GSM call termination service based on VoIP Technology.