... -in wireless modules can be inserted SIM cards, simultaneously to send text messages. Key Features♦USB/RS232 GSM modem pool♦Based ... SIM card(big/small) slots♦Comply with GSM phase2 standard♦Send and receive SMS,MMS ♦Maximum transmitting speed 115KBps♦Input voltage ... -in wireless modules can be inserted SIM cards, simultaneously to send text messages. serial port gsm modem serial port gsm modem ...