AP-N1-GSM2S4 GSM VoIP Module is a new 2-Port GSM Module(4 SIM card slots per GSM Port) for GSM Call Termination Service. AP-N1-GSM2S4 GSM VoIP Module can be installed in our next generation AddPac GSM Gateway N1 Hardware Platform such as AP-GS3800, AP-GS3000, AP-GS2800, AP-GS2700, AP-GS25000, etc. This GSM VoIP Module supports Quad-Band (850/900/1800/1900MHz) GSM frequency, Four(4) SIM card slots per GSM port, Hot-Swap Switch Button, Two(2) GSM Antenna Interface. This GSM module have eight(8) GSM SIM card slots internally. Also this module supports the Voice DSP for GSM call termination service based on VoIP Technology.