GSM MODEM POOL also known as "SMS cat pool" “Bulk sms machine” in China, With the USB 2.0 Cable connect with computer (laptops, desktops), insert both big and small sim cards, open our bulk sms software, then can send and receiving mass messages, simultaneously to send 600 pieces messages per hour for one port, totally 4800 for all 8 ports. Internal adapter assure stable voltage and excellent working environment.