AP-N1-GSM4S8 GSM VoIP Module is a new 4-Port GSM Module (8 SIM card slots per GSM Port) for GSM Call Termination Service. AP-N1-GSM4S8 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, Eight(8) SIM card slots per GSM port, Hot-Swap Switch Button, One(1) GSM Antenna Interface. This GSM module has thirty-two(32) GSM SIM card slots internally. Also this module supports the Voice DSP for GSM call termination service based on VoIP Technology.